Background info: My aluminum MacBook (late 2008) came with Leopard, and when I first got it I ran the migration assistant to bring over all my user data (not applications) from an old PowerBook G4 that was running Tiger. Tihs previous powerbook was migrated to from an old iMac. So that was two migrations of data between multiple Macs, and no clean installs were done. Fast forward to my current MacBook, about 6 months ago I finally upgraded from Leopard to Snow Leopard. Lately I have noticed my MacBook running a bit less "snappy" when launching apps and just general processing. I also think it is causing to e battery to drain a bit faster being that it is having a harder time finding data to process. I am not a power user, so mainly I use it for email, internet, iTunes, and streaming media to my Apple TV. In any case, it makes me think that a clean install of Snow Leopard (or maybe even Lion) might be a good idea. However I am not sure if this would help, nor how to go about it. FYI...my 160GB HD currently has 90GB free space. Also, I regularly use time machine to back-up all my data. Questions: 1. So, if this perceived slowness is due to the build-up of junk files on my HD, if I were to erase my HD, and then restore from my most recent time machine back-up, would it bring back these alleged junk files? 2. If we assume for the sake of discussion that I also have fragmentation, would the method described in question number 1 actually solve this fragmentation? Meaning, if there are currently large chunks of unused data scattered all over my HD causing it to perform inefficiently, is it just going to restore my HD exactly as it was, and therefore not eliminate the fragmentation problems? Thanks in advance!