The following OpenGL features are not supported at this time: overlays, stereo, hardware-accelerated indirect rendering.
OpenGL-like functionality is provided with the Mesa library. XFree86 4.0 uses a beta version Mesa 3.3. When newer versions of Mesa are available, the 3D drivers can be updated without reinstalling XFree86 or libGL.so.
The GLX 1.3 API is exported but none of the new 1.3 functions are operational.
The new glXGetProcAddressARB function is fully supported.
There are several understood, but unresolved problems relating to hardware locking and signal handling. Hitting CTRL-z to suspend a 3D application can sometimes cause the X server to lock-up if executing device driver code at that moment. Also, using a debugger to step through OpenGL/Mesa device driver functions code could cause a lock-up. These problems will be fixed in the future.
When you run multiple GL applications at once you may notice poor time slicing. This is due to an interaction problem with the Linux scheduler which will be addressed in the future.
The DRI bug database which includes bugs related to specific drivers is at the SourceForge DRI Bug Database
Please scan both the open and closed bug lists to determine if your problem has already been reported and perhaps fixed.