I have this weird problem with my Mac. It sometimes seems to ‘slow down’ randomly. Screen refreshing slows way down and sometimes a process running in an application slows down. What’s weirder is that in every case I can ‘revive’ it by simply moving the mouse a bit. What causes this?”
Depending upon your model of Macintosh this is most likely caused by a function known as processor cycling. Processor cycling is designed primarily for portable computers to conserve battery power (though it is available in many Mac desktop machines). It basically slows the processor down during periods of apparent inactivity. Unfortunately it is not always smart enough to realize that the computer may be working on something you need. It tends to pay more attention to user input than on processes that may be running internally. The technical reasons for this are significant, but unimportant in this context. Unless you need to conserve power you should turn this function off. You can find it under the advanced settings in the Energy Saver Control Panel.