my just on this is that it depends what you're running in the background. If you have your web browser open or something and you're viewing youtube videos, close them. Whenever I open up youtube while the game is running it slows down and starts to judder, as in system lag. Close it, and its back to normal.
I closed the youtube tabs on my browser and loaded the game up again and it was fine. It could be a bandwidth issue, but whatever it is I find it screws up when i'm running too many other things. Especially anything that uses flash (e.g youtube).
Edited, Oct 8th 2010 1:40pm by Duresthar