The BZFlag fest last weekend was the first time I had used the 3D capabilities on my AMD R600 based card continuously for an extended period (e.g. more than an hour). The good news it worked. The bad news I had several GPU lock ups. In most cases the kernel driver's watch dog timer detected the lock up and reset the GPU, but on two occasions this safety feature failed and I had to hit the big red button.
After the second hard lock up, I checked Debian experimental for updates to the various libraries I am using to get the R600 to work. Lo and behold! There were several! I did not have another lock up after installing the updates, but this may just have been a fluke. It is hard to tell if the updates actually had any effect at all, really.
I must remember to check for updates in experimental regularly as it is not handled automatically by the package management system. This is a small safety feature as experimental packages could easily trash your system. This is life with Debian experimental.