I’m telling you this because nobody ever told me: run maintenance on your Mac. Defragging doesn’t exist for Macs, at least not in so many words. But data is still misplaced, and if left untended it can cause your computer to crash. Two years after getting my old Powerbook, I had to have the hard drive replaced because it was just fried. Lucky that it was still under warranty, but not so lucky the fact that I lost everything on it (backing things up: also important).
To avoid this, once a month or more you should open ‘Disk Utility’ (it’s in the Utility folder, in Applications) and run all three of the options on your computer (verify disk permissions, repair disk permissions, and verify disk). Even better, download a maintenance program like mainmenu.
I hope this saves somebody some pain.