using the new firmware
(http://people.freedesktop.org/~agd5f/radeon_ucode/ucode.tar.gz) didn't seem to
make a change in stability:

starting in fluxbox
+ firefox
+ gnote

watching videos on youtube (adobe flash player) for several minutes, writing
some notes in gnote, exiting; gmail, google+

starting in Xfce4+ compiz-fusion, exiting

starting in fluxbox
+ firefox
+ gnote

browsing, watching wallpapers, gmail, google+

text corruption, especially in gmail & google search results occured with:

radeon 0000:01:00.0: Packet0 not allowed!

couldn't pinpoint what triggered it, several occurences in dmesg

starting up chromium, browsing youtube (adobe flash explicitly disabled),
wanted to watch a video (HTML5 video), screen doesn't react anymore, turns
black

gpu/screen turns black, hardlock

will attach dmesg later, no suspicious content besides

radeon 0000:01:00.0: Packet0 not allowed!

any useful data in connection with chromium -> hardlock, all data lost