I’m not at all familiar with MobileMe and applesyncnotifier, but a lot of processes that are supposed to automatically synchronize or update stuff over the internet or a network tend to use a lot of processor power even when it’s just waiting for something to do. For this reason, I generally disable anything automatic that I can do manually, as long as it won’t cause any significant inconvenience. You may want to search around the net and see if you can find a way to disable the process more permanently, if your situation is similar.