Finally, here is a diff that I've used to upload a new version to Ubuntu
precise which includes the Python 3 packaging.  Hopefully, you'll find it
helpful for updating the Debian packaging; I'm interested in your feedback for
this as well.  I omitted the quilt patches and debian/changelong entry I used
since they won't be relevant to Debian, or after you release the merged the
`python3` branch.

This also enables the test suite during the build, since that works now in
precise.

Apologies for pasting the diff here.  Bugzilla rejected my attachment and I
can't log into it atm.

=== modified file 'debian/control'
--- debian/control	2011-07-25 12:51:22 +0000
+++ debian/control	2012-01-12 15:45:43 +0000
@@ -1,22 +1,32 @@
 Source: dbus-python
 Section: devel
 Priority: optional
-Maintainer: Utopia Maintenance Team <email address hidden>
+Maintainer: Ubuntu Developers <email address hidden>
+XSBC-Original-Maintainer: Utopia Maintenance Team <email address hidden>
 Uploaders: Sjoerd Simons <email address hidden>,
            Sebastian Dröge <email address hidden>,
            Simon McVittie <email address hidden>,
            Loic Minier <email address hidden>
-Build-Depends: debhelper (>= 8),
-               xmlto,
-               python-all-dev (>= 2.6.6-3~),
-               python-all-dbg (>= 2.6.6-3~),
+Build-Depends: autoconf,
+               automake,
+               autotools-dev,
+               debhelper (>= 8),
                libdbus-1-dev (>= 1.4),
                libdbus-glib-1-dev (>= 0.71),
-               autotools-dev
-Build-Depends-Indep: python-docutils,
-                     python-epydoc (>= 3.0~beta1)
+               libtool,
+               python-all-dbg (>= 2.6.6-3~),
+               python-all-dev (>= 2.6.6-3~),
+               python-gobject,
+               python-gobject-dbg,
+               python3-all-dbg,
+               python3-all-dev,
+               python3-gobject,
+               python3-gobject-dbg,
+               xmlto
+Build-Depends-Indep: python-docutils, python-epydoc (>= 3.0~beta1)
 Standards-Version: 3.9.2
-X-Python-Version: >= 2.4
+X-Python-Version: >= 2.6
+X-Python3-Version: >= 3.2
 XS-Dm-Upload-Allowed: yes
 Homepage: http://www.freedesktop.org/wiki/Software/DBusBindings#Python
 Vcs-Git: git://anonscm.debian.org/git/pkg-utopia/dbus-python.git
@@ -25,16 +35,12 @@
 Package: python-dbus
 Section: python
 Architecture: any
-Depends: ${shlibs:Depends},
-         ${misc:Depends},
-         ${python:Depends}
+Depends: ${misc:Depends}, ${python:Depends}, ${shlibs:Depends}
 Recommends: python-gobject | python-gtk (<< 2.10)
-Suggests: python-dbus-doc, python-dbus-dbg
+Suggests: python-dbus-dbg, python-dbus-doc
 Replaces: python2.4-dbus
 Conflicts: python2.4-dbus
-Breaks: gnome-osd (<< 0.12.0),
-        gajim (<< 0.11.1),
-        python-qt4-dbus (<< 4.8.3-3)
+Breaks: gajim (<< 0.11.1), gnome-osd (<< 0.12.0), python-qt4-dbus (<< 4.8.3-3)
 Provides: ${python:Provides}
 Description: simple interprocess messaging system (Python interface)
  D-Bus is a message bus, used for sending messages between applications.
@@ -45,11 +51,23 @@
  .
  See the dbus description for more information about D-Bus in general.
 
+Package: python-dbus-common
+Section: python
+Priority: extra
+Architecture: any
+Depends: ${misc:Depends}, ${python:Depends}, ${shlibs:Depends}
+Description: Common files for dbus-python.
+Conflicts: python-dbus (<< ${source:Version})
+
 Package: python-dbus-dbg
 Section: debug
 Priority: extra
 Architecture: any
-Depends: python-dbus (= ${binary:Version}), python-dbg, ${shlibs:Depends}, ${misc:Depends}
+Depends: python-dbg,
+         python-dbus (= ${binary:Version}),
+         python-dbus-common,
+         ${misc:Depends},
+         ${shlibs:Depends}
 Description: Debug build of the D-Bus Python interface
  This package provides a version of the python-dbus package built for
  debugging versions of Python.
@@ -62,3 +80,34 @@
 Description: Documentation for the D-Bus Python interface
  This package provides text and HTML documentation, and examples, for the
  python-dbus package.
+
+Package: python3-dbus
+Section: python
+Architecture: any
+Depends: python-dbus-common,
+         ${misc:Depends},
+         ${python:Depends},
+         ${shlibs:Depends}
+Recommends: python-gi
+Suggests: python-dbus-dbg, python-dbus-doc
+Provides: ${python:Provides}
+Description: simple interprocess messaging system (Python interface)
+ D-Bus is a message bus, used for sending messages between applications.
+ Conceptually, it fits somewhere in between raw sockets and CORBA in
+ terms of complexity.
+ .
+ This package provides a Python interface to D-Bus.
+ .
+ See the dbus description for more information about D-Bus in general.
+
+Package: python3-dbus-dbg
+Section: debug
+Priority: extra
+Architecture: any
+Depends: python3-dbg,
+         python3-dbus (= ${binary:Version}),
+         ${misc:Depends},
+         ${shlibs:Depends}
+Description: Debug build of the D-Bus Python interface
+ This package provides a version of the python-dbus package built for
+ debugging versions of Python.
\ No newline at end of file

=== added file 'debian/python-dbus-common.install'
--- debian/python-dbus-common.install	1970-01-01 00:00:00 +0000
+++ debian/python-dbus-common.install	2012-01-12 14:04:25 +0000
@@ -0,0 +1,2 @@
+debian/tmp/usr/include/*
+debian/tmp/usr/lib/pkgconfig/*

=== added file 'debian/python-dbus-dbg.install'
--- debian/python-dbus-dbg.install	1970-01-01 00:00:00 +0000
+++ debian/python-dbus-dbg.install	2012-01-12 14:04:25 +0000
@@ -0,0 +1,1 @@
+debian/python-dbus-2*-dbg/usr/lib/python2.*/*-packages/*

=== added file 'debian/python-dbus.install'
--- debian/python-dbus.install	1970-01-01 00:00:00 +0000
+++ debian/python-dbus.install	2012-01-12 14:04:25 +0000
@@ -0,0 +1,1 @@
+debian/tmp/usr/lib/python2.*/*-packages/*

=== added file 'debian/python3-dbus-dbg.install'
--- debian/python3-dbus-dbg.install	1970-01-01 00:00:00 +0000
+++ debian/python3-dbus-dbg.install	2012-01-12 14:04:25 +0000
@@ -0,0 +1,1 @@
+debian/python-dbus-3*-dbg/usr/lib/python3/*-packages/*

=== added file 'debian/python3-dbus.install'
--- debian/python3-dbus.install	1970-01-01 00:00:00 +0000
+++ debian/python3-dbus.install	2012-01-12 14:04:25 +0000
@@ -0,0 +1,1 @@
+debian/tmp/usr/lib/python3/*-packages/*

=== modified file 'debian/rules'
--- debian/rules	2011-07-25 12:51:22 +0000
+++ debian/rules	2012-01-12 15:51:20 +0000
@@ -3,6 +3,8 @@
 # Copyright © 2003 Daniel Stone <email address hidden>
 # Copyright © 2006 Sjoerd Simons <email address hidden>
 
+DH_VERBOSE=1
+
 # These are used for cross-compiling and for saving the configure script
 # from having to guess our platform (since we know it already)
 DEB_HOST_GNU_TYPE   ?= $(shell dpkg-architecture -qDEB_HOST_GNU_TYPE)
@@ -13,6 +15,9 @@
 PYVERS := $(shell pyversions --requested --version debian/control)
 PYDEFAULTVER := $(shell pyversions --default --version)
 
+PY3VERS := $(shell py3versions --requested --version debian/control)
+PY3DEFAULTVER := $(shell py3versions --default --version)
+
 ifeq ($(DEB_BUILD_GNU_TYPE),$(DEB_HOST_GNU_TYPE))
 	CONFIGURE_FLAGS += --build=$(DEB_BUILD_GNU_TYPE)
 else
@@ -47,6 +52,9 @@
 build-%/build-stamp: build-%/configure-stamp
 	dh_testdir
 	PYTHON=/usr/bin/python$* $(MAKE) -C build-$*
+ifeq (,$(findstring nocheck,$(DEB_BUILD_OPTIONS)))
+	$(MAKE) -C build-$* check
+endif
 	touch $@
 
 build-doc/build-doc-stamp: build-doc/configure-stamp
@@ -56,7 +64,12 @@
 
 build: build-arch
 #build: build-indep
-build-arch: $(PYVERS:%=build-%/build-stamp) $(PYVERS:%=build-%-dbg/build-stamp)
+
+build-arch: $(PYVERS:%=build-%/build-stamp) \
+	    $(PYVERS:%=build-%-dbg/build-stamp) \
+	    $(PY3VERS:%=build-%/build-stamp) \
+	    $(PY3VERS:%=build-%-dbg/build-stamp)
+
 build-indep: build-doc/build-doc-stamp
 
 install-clean:
@@ -64,40 +77,40 @@
 	dh_testroot
 	dh_prep
 
-install-%: build-%/build-stamp
+install-%:
 	dh_testdir
 	dh_testroot
-	$(MAKE) -C build-$* install DESTDIR=$(CURDIR)/debian/python-dbus
+	$(MAKE) -C build-$* install DESTDIR=$(CURDIR)/debian/tmp
 	# keep a copy of /usr/include/debian-python.h and
 	# /usr/lib/pkgconfig/debian-python.pc to verify they match later
-	cp debian/python-dbus/usr/include/dbus-1.0/dbus/dbus-python.h debian/tmp-$*.h
-	cp debian/python-dbus/usr/lib/pkgconfig/dbus-python.pc debian/tmp-$*.pc
+	cp debian/tmp/usr/include/dbus-1.0/dbus/dbus-python.h debian/tmp-$*.h
+	cp debian/tmp/usr/lib/pkgconfig/dbus-python.pc debian/tmp-$*.pc
 
-dbg-install-%: build-%-dbg/build-stamp
+dbg-install-%:
 	dh_testdir
 	dh_testroot
-	$(MAKE) -C build-$*-dbg install DESTDIR=$(CURDIR)/debian/python-dbus-dbg
-	find debian/python-dbus-dbg ! -type d ! -name '*.so' -print0 | xargs -0 rm -f
-	find debian/python-dbus-dbg -depth -empty -exec rmdir {} \;
+	$(MAKE) -C build-$*-dbg install DESTDIR=$(CURDIR)/debian/python-dbus-$*-dbg
+	find debian/python-dbus-$*-dbg ! -type d ! -name '*.so' -print0 | xargs -0 rm -f
+	find debian/python-dbus-$*-dbg -depth -empty -exec rmdir {} \;
+	for i in $$(find debian/python-dbus-$*-dbg -name '*.so'); do \
+		b=$$(basename $$i .so); \
+		mv $$i $$(dirname $$i)/$${b}_d.so; \
+	done
 
-install-arch: build-arch install-clean $(PYVERS:%=install-%) $(PYVERS:%=dbg-install-%)
-	rm -f debian/python-dbus/usr/lib/python*/*-packages/*.la
-	rm -rf debian/python-dbus/usr/share/doc/deleteme
-	rm -f debian/python-dbus-dbg/usr/lib/python*/*-packages/*.la
-	rm -rf debian/python-dbus-dbg/usr/share/doc/deleteme
+install-arch: build-arch install-clean \
+	      $(PYVERS:%=install-%) $(PYVERS:%=dbg-install-%) \
+	      $(PY3VERS:%=install-%) $(PY3VERS:%=dbg-install-%)
+	rm -f debian/tmp/usr/lib/python*/*-packages/*.la
+	rm -rf debian/tmp/usr/share/doc/deleteme
 	# compare installed .pc and .h, asserting that the ones all versions
 	# wanted are the same as what we ended up with
-	for v in $(PYVERS); do \
-		diff --brief debian/python-dbus/usr/include/dbus-1.0/dbus/dbus-python.h \
+	for v in $(PYVERS) $(PY3VERS); do \
+		diff --brief debian/tmp/usr/include/dbus-1.0/dbus/dbus-python.h \
 			debian/tmp-$$v.h || exit 1; \
-		diff --brief debian/python-dbus/usr/lib/pkgconfig/dbus-python.pc \
+		diff --brief debian/tmp/usr/lib/pkgconfig/dbus-python.pc \
 			debian/tmp-$$v.pc || exit 1; \
 	done
 	rm -f debian/tmp-*.pc debian/tmp-*.h
-	for i in $$(find debian/python-dbus-dbg -name '*.so'); do \
-		b=$$(basename $$i .so); \
-		mv $$i $$(dirname $$i)/$${b}_d.so; \
-	done
 
 clean::
 	dh_testdir
@@ -141,7 +154,8 @@
 	dh_link -s
 	dh_compress -s -X.py -X.js
 	dh_fixperms -s
-	dh_python2 -s
+	dh_python2 -s -v
+	dh_python3 -s -v
 	dh_installdeb -s
 	dh_shlibdeps -s
 	dh_gencontrol -s
@@ -149,4 +163,6 @@
 	dh_builddeb -s
 
 binary: binary-arch binary-indep
+	autoreconf
+
 .PHONY: build clean binary-indep binary-arch binary install-arch install-clean