DRI2 will solve problems with using 3d and video playback while using compiz or another compositor, eliminating the chronic flicker and tearing caused by drawing conflicts.
Later on, DRI2 is supposed to also have a mechanism to prevent tearing. Right now, the radeon driver (from git) has their own custom solution which is said to pretty much get rid of tearing.
Thanks for the info bridgman. So essentially, more and more stuff is being pulled out of the Xserver to make it work more cleanly. Maybe someday X will be nothing more than a display manager. That certainly seems to be the trend.
I really like the design of Gallium3D (as much as I can understand it). I hope work on radeon drivers for Gallium3D can be commenced in earnest (I'm guessing that it will happen when there's a basic old-style Mesa driver for new cards and the bugs are cleaned up in DRI2, KMS, GEM and the new hardware development branches.)