http://bugs.winehq.org/show_bug.cgi?id=10878
--- Comment #2 from Nick Lawson vektuz@cox.net 2007-12-30 13:50:30 --- I retested in 0.9.52 It still happens in both compiz mode, and vmware mode, but in true native (no-compiz mode), this does not happen.
It happens to windows machines on vmware too, and on windows machines through VNC, so its probably a steam bug. Either that, or a combination of WINE+VMWARE or a funky display driver, or compiz, is redrawing/repolling the steam window constantly causing it to eat CPU. I spoke to valve about it directly a couple months ago, (because people were seeing this on windows/AMD machines natively, and they said it was because of something constantly polling the window for some reason).
Minimizing the steam window seems to make this go away, so it at least doesn't stop you from playing your games, as long as you remember to minimize the window on game launch. Otherwise it slows the game down immensely.