I have a problem with Portal for Linux. It's like I'm having a big input lag. I move the mouse and it takes about half a second until the screen follows that input. The thing is, with the open-source (radeon) driver, I don't have the problem at all and it runs really smooth.
The problem occurs with Catalyst 13.4, Arch Linux 64bit, Radeon HD 6670, Kernel 3.8. Left 4 Dead 2 is just fine, but Portal is not.