More noticeable in multiplayer, the performance of the current beta release is dreadful. It seems fine in some of the showcases, but load a custom map with unit or join a multiplayer game and the FPS drops to 6-8.
I running quite a beefy system, not the fastest out there but certainly faster than the majority of users.
GeForce GTX 480 (1680x1050)
AMD Phenom II X4 840
16GB RAM
I have checked and there is no CPU bottlenecks and testing my video card in numerous utilities shows it to be in spec and working fine.