On a similar note ... running a 4850 - 9.5 drivers, (with a multi-core system) on Fedora 10. I've experienced lockups when all cores are configured to 'ondemand' cpufreq.
If I set just one of my cores to 'performance' it appears to alleviate this issue. Perhaps this is similar to disabling the cpufreq management? Puzzling all the same, I agree.