actually this was the 1st time actual internal catlyst drivers were leaked by ATI, these are not OEM drivers like some that have popped up.
I threw em on my system and they are running pretty good. It was said there wasnt going to be a big performance boost in these drivers like there was in the 3.4 drivers, mostly compatability and stability improvements. I threw em on and they are running fine, the one thing i noticed is that some of the display corruption problems seem to be resolved. I had some problems sometimes after i rebooted that I would get left over garbage in my video memory causing garbled displays, which was easily fixed by cutting the power to my system and turning it back on.
The official 3.5 catalyst drivers will be released monday June23rd.