I just tried the latest git code. I must say, impressive work Thanks Alex. All the corruptions gone. I can enable Desktop Effects on kde 4.1.3 with Xrender and Disable Functionality Check options.
Here some feedback about speed. With composite the performance is worse. Scrolling is not usable. Window drawings are less responsive (if this is correct word for it, excuse my english). Without composite, the overall performanse is good enough. Not fast as radeonhd driver anyway but it is usable. The scrolling it absolutely far better than yesterdays build it gives me nearly the same taste of performance as radeonhd driver. So I have no real complain about scrolling as before. I didn't tried XV video yet.
So, again thanks. Keep up good work
Edit: more feedback about performance
It takes about 2 seconds in fireforx to switch tabs and now after abit longer test scrolling seems not that fast. And switching windows on desktop is taking more, about 3 sec to render window contends. Yang Zhao posted a patch to mail-list about R600OverlapCopy() optimisation. I am going to test it now.