If you're suffering of MobileMe sync eating up 100% CPU on Mac OS X and the sync wheel running for a long time, check if there is a "synchronization warning" window in the background. That is the window that warns you when more than X percent of calendar entries are changing. It is easily lost behind other application windows.
When that window is open on any of your computers (waiting for you to click), apparently nobody can sync and MobileMe will take 100% CPU while it's trying.
Apple really should fix this by a) not eating up 100% CPU in any situation and b) forcing the warning window to the top so you can see it.