I try not to reformat if I can help it. I have a lot of games installed and an ever-expanding music collection, not to mention tons of photos, so it really is a pain for me to do it frequently. I only reformat if I have to, and I haven't needed to in a very long time (and I intend to keep it that way). Running CCleaner a lot, defragmenting often and avoiding installations if I don't have to (I try to only use portable software, except for things like anti-virus, MS Office, Firefox, etc). My computer is by no means at peak performance, but it still works very well.