My 24" imac has the standard 640 gig hard drive. Disc utility says that I have used 292 gigs. I have gone through all m files and folders and can only account for 157.15 gigs. I tried running onyz expecting the culprit was a bunch of junk that has gathered over time. Afterwards, I still had the same 292 gigs of used space and can only account 157.15 gigs. A complet format and reinstall will obviously solve this problem but I don't want to go to that extreme If its not really required.