When entering the server browser, my frame rate drops like a rock (>4fps). My character in the background is very jerky, which isn’t a problem. What is a problem is that my mouse also has crazy input lag. Its very hard to scroll or sort the list or do anything. The problem doesn’t stop when the list is finished refreshing.
The rest of the game menus, offline and online play work fine. Once I am in a game I can pretty much play as expected (<25fps). It’s just the server browser that is nearly unusable. Here is a thread on the Steam forums with other users experiencing the same issue : http://forums.steampowered.com/forums/showthread.php?p=22332573