I'm seeing this bug too, with my laptop Radeon Mobility 9600 card.

After the upgrade of xserver-xorg, within a few hours seemingly at
random, the X server crashes and brings down the entire system with it
(including networking).  This is a regression from 6.8.2.dfsg.1-11,
which is stable on the same machine, even with everything else at
6.9.0.

I've attached my xorg.conf and /var/log/Xorg.0.log files with
6.9.0.dfsg.1-1 temporarily installed again.  I tried commenting out
the 'Load "dri"' line, which didn't get rid of the crashes.

-- System Information:
Debian Release: testing/unstable
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.6.15-1-686
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8)

Versions of packages xserver-xorg depends on:
ii  debconf [debconf-2.0]     1.4.67         Debian configuration management sy
ii  libc6                     2.3.5-11       GNU C Library: Shared libraries an
ii  libgcc1                   1:4.0.2-5      GCC support library
ii  libxau6                   6.9.0.dfsg.1-1 X Authentication library
ii  libxdmcp6                 6.9.0.dfsg.1-1 X Display Manager Control Protocol
ii  xserver-common            6.9.0.dfsg.1-1 files and utilities common to all 
ii  zlib1g                    1:1.2.3-9      compression library - runtime

Versions of packages xserver-xorg recommends:
ii  discover                  2.0.7-2.1      hardware identification system
ii  laptop-detect             0.12.1         attempt to detect a laptop
ii  mdetect                   0.5.2.1        mouse device autodetection tool
ii  xlibs                     6.9.0.dfsg.1-1 X Window System client libraries m
ii  xresprobe                 0.4.18-1       X Resolution Probe

-- debconf information:
  xserver-xorg/multiple_possible_x-drivers:
  xserver-xorg/config/monitor/use_sync_ranges: true
* xserver-xorg/config/inputdevice/mouse/port: /dev/input/mice
  xserver-xorg/config/monitor/lcd: false
  xserver-xorg/autodetect_monitor: true
* xserver-xorg/config/display/modes: 1280x800, 1024x768, 800x600, 640x480
  xserver-xorg/config/display/default_depth: 24
  xserver-xorg/config/inputdevice/keyboard/internal:
* xserver-xorg/config/inputdevice/keyboard/options:
  xserver-xorg/config/inputdevice/mouse/zaxismapping: true
* xserver-xorg/config/device/use_fbdev: false
* xserver-xorg/config/inputdevice/keyboard/variant:
  xserver-xorg/config/nonnumeric_string_error:
  xserver-xorg/config/inputdevice/keyboard/layout: fr-latin9
  xserver-xorg/config/monitor/identifier: Écran générique
  xserver-xorg/config/inputdevice/mouse/emulate3buttons: true
* xserver-xorg/autodetect_mouse: true
  xserver-xorg/config/monitor/horiz-sync: 30-67
  xserver-xorg/config/monitor/range_input_error:
  xserver-xorg/config/write_dri_section: true
* xserver-xorg/config/inputdevice/keyboard/model: pc105
* xserver-xorg/config/device/driver: ati
  xserver-xorg/config/monitor/selection-method: Medium
  xserver-xorg/config/write_files_section: true
  xserver-xorg/config/monitor/mode-list: 640x480 @ 60Hz
  xserver-xorg/config/doublequote_in_string_error:
  xserver-xorg/config/monitor/screen-size: 17 inches (430 mm)
* shared/default-x-server: xserver-xorg
  xserver-xorg/config/inputdevice/mouse/protocol: ImPS/2
* shared/no_known_x-server:
  xserver-xorg/config/device/bus_id_error:
  xserver-xorg/config/monitor/vert-refresh: 30-60
  xserver-xorg/config/fontpath/fontserver:
  xserver-xorg/config/modules: bitmap, dbe, ddc, dri, extmod, freetype, glx, int10, record, type1, v4l, vbe
  xserver-xorg/config/device/video_ram:
  xserver-xorg/config/device/identifier: Carte vidéo générique
  xserver-xorg/config/null_string_error:
  shared/multiple_possible_x-servers:
* xserver-xorg/config/device/bus_id: PCI:1:0:0
* xserver-xorg/autodetect_video_card: true
* xserver-xorg/config/inputdevice/keyboard/rules: xorg