This one has bothered me for a long time. The solution is, of course, simple. But, I still don't understand why was it necessary to force users to search so hard for this piece of information, where all the older X server releases worked OK out of the box?
If you find that after upgrading to X.Org 7.3 your display becomes very slow, and you own ATI Radeon, all you need to do is to put this line in the Device section of your
Option "MigrationHeuristic" "greedy"