Framerate dropping, using more and more memory

[MattF]

I observed the exact same thing and turning off aero seemed to stop it, although I've only played about 40 minutes with it off so far. Might be worth a try?

edit: Just played a further 20 minutes, still hasn't happened again. Note that aero appeared to automatically turn off when launching the game for me too, but turning it off manually still seems to have fixed the issue.