On the latest driver on ubuntu maverick 32bit (on 64bit cpu, i use very memory heavy stuff, so I save some mem by going 32bit).
Assertion failed in ../../../../../../../../drivers/2d/lnx/fgl/drm/kernel/hal_evergreen.c at line: 64
I got a complete X hang while clicking a folder on the toolbar in google chrome. Tabbing out to console and killall -9 chrome left me with a usable system. Until i started chrome and clicked a folder on the toolbar again. Found that assertion in dmesg.
I have been using the driver for some time and never seen it before. I fairly recently added hpet=disable to my boot to try to debug a slowdown after suspend to ram (which happens every week or so, and therefor isn't too easy to debug). Mentioning in case it's related.