time machine is definitely nice. When i got my apple i got a brand new external just to use for it, but for the first week i could never get it to run all the way, it would always lock up after about 10 minutes and say the disc was ejected... then i ran into this article on how to properly get set up, then it ran fast and perfect
give it a read
http://support.apple.com/kb/TS1550
enjoy