For what it's worth, I had kde-window-decorator also just crashing, right after "compiz --replace" from ALT-F2.

I had compiz running before, switched to virtual console 1, back to 7, which was very slow then. So I've tried "compiz --replace" again, which caused this crash then.

Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread -1226815280 (LWP 9149)]
[KCrash handler]
#6  0xb72f386e in QObject::parent (this=0x18) at ../include/qobject.h:154
#7  0xb72f403f in QWidget::parentWidget (this=0x18, sameWindow=false)
    at ../include/qwidget.h:878
#8  0xb740790b in ~QWidget (this=0x814ed78) at kernel/qwidget.cpp:946
#9  0xb7468b33 in ~QButton (this=0x814ed78) at widgets/qbutton.cpp:410
#10 0xb7c6b791 in ~KCommonDecorationButton (this=0x814ed78)
    at /build/buildd/kdebase-3.5.7/./kwin/lib/kcommondecoration.cpp:887
#11 0xb6c03667 in ~QuartzButton (this=0x814ed78)
    at /build/buildd/kdebase-3.5.7/./kwin/clients/quartz/quartz.cpp:393
#12 0xb7c6e3b4 in ~KCommonDecoration (this=0x8161c78)
    at /build/buildd/kdebase-3.5.7/./kwin/lib/kcommondecoration.cpp:55
#13 0xb6c06b3d in ~QuartzClient (this=0x8161c78)
    at /build/buildd/kdebase-3.5.7/./kwin/clients/quartz/quartz.h:71
#14 0x0805980d in KWD::Window::reloadDecoration (this=0x814dbd0)
    at ../../../kde/window-decorator/window.cpp:1503
#15 0x0805499d in KWD::Decorator::changeShadowOptions (this=0x806e0f8, 
    opt=0xbfe66f40) at ../../../kde/window-decorator/decorator.cpp:478
#16 0x08054f7c in dbusHandleMessage (connection=0x8162808, message=0x8137f08, 
    userData=0x806e0f8) at ../../../kde/window-decorator/decorator.cpp:183
#17 0xb7ed7c22 in dbus_connection_dispatch () from /usr/lib/libdbus-1.so.3
#18 0xb7c58893 in DBusQt::Connection::dispatchRead ()
   from /usr/lib/libdbus-qt-1.so.1
#19 0xb7c59147 in DBusQt::Connection::qt_invoke ()
   from /usr/lib/libdbus-qt-1.so.1
#20 0xb73ca893 in QObject::activate_signal (this=0x8146310, clist=0x81442f8, 
    o=0xbfe670ec) at kernel/qobject.cpp:2356
#21 0xb73cb338 in QObject::activate_signal (this=0x8146310, signal=2)
    at kernel/qobject.cpp:2325
#22 0xb7c59b29 in DBusQt::Internal::Integrator::readReady ()
   from /usr/lib/libdbus-qt-1.so.1
#23 0xb7c59c0f in DBusQt::Internal::Integrator::slotRead ()
   from /usr/lib/libdbus-qt-1.so.1
#24 0xb7c59c8a in DBusQt::Internal::Integrator::qt_invoke ()
   from /usr/lib/libdbus-qt-1.so.1
#25 0xb73ca893 in QObject::activate_signal (this=0x8140f48, clist=0x815d050, 
    o=0xbfe67238) at kernel/qobject.cpp:2356
#26 0xb73cb1aa in QObject::activate_signal (this=0x8140f48, signal=2, 
    param=10) at kernel/qobject.cpp:2449
#27 0xb775767f in QSocketNotifier::activated (this=0x8140f48, t0=10)
    at .moc/debug-shared-mt/moc_qsocketnotifier.cpp:85
#28 0xb73ed46e in QSocketNotifier::event (this=0x8140f48, e=0xbfe67568)
    at kernel/qsocketnotifier.cpp:258
#29 0xb7361af0 in QApplication::internalNotify (this=0x806e0f8, 
    receiver=0x8140f48, e=0xbfe67568) at kernel/qapplication.cpp:2635
#30 0xb736391f in QApplication::notify (this=0x806e0f8, receiver=0x8140f48, 
    e=0xbfe67568) at kernel/qapplication.cpp:2358
#31 0xb7e3a242 in KApplication::notify (this=0x806e0f8, receiver=0x8140f48, 
    event=0xbfe67568)
    at /build/buildd/kdelibs-3.5.7/./kdecore/kapplication.cpp:550
#32 0xb72f4209 in QApplication::sendEvent (receiver=0x8140f48, 
    event=0xbfe67568) at ../include/qapplication.h:520
#33 0xb7353ee9 in QEventLoop::activateSocketNotifiers (this=0x8079938)
    at kernel/qeventloop_unix.cpp:578
#34 0xb7308d2b in QEventLoop::processEvents (this=0x8079938, flags=4)
    at kernel/qeventloop_x11.cpp:383
#35 0xb737c1ce in QEventLoop::enterLoop (this=0x8079938)
    at kernel/qeventloop.cpp:198
#36 0xb737bfde in QEventLoop::exec (this=0x8079938)
    at kernel/qeventloop.cpp:145
#37 0xb7363699 in QApplication::exec (this=0x806e0f8)
    at kernel/qapplication.cpp:2758
#38 0x080540bf in main (argc=) at ../../../kde/window-decorator/main.cpp:131
#39 0xb79f7050 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
#40 0x08051861 in _start ()