I've got an iMac (1.83GHz Intel Core 2 Duo, 2GB SDRAM) running Snow Leopard (10.6.3). It's running the usual sort of stuff (Mac Office, Evernote, Itunes, Time Machine etc). Problem: If it has been left on for a while (eg. overnight) it very often gets very sluggish to the extent that I have to restart it - this solved the problem... for another few hours. I have iStatPro installed as a widget and when the problem arrises, that shows massive CPU usage by the user leaving only 1 or 2% free. When I look in activity monitor, I can't see anything that is using those sorts of resources. I was thinking on reformatting and restoring from time machine (it's in my blood - I used to have a PC), but has anyone got any better ideas?