…and I am here to testify.
My (MacBook Pro) disk drive got flaky a week ago, making odd noises and refusing to do its disk-drive things (like read the disk). Last Saturday I carted it down to the Apple Store, where they agreed that It Shouldn’t Do That, and also agreed to fix my crunchy trackpad button, a long-standing annoyance.
I picked it up on Tuesday, restored from my last Time Machine backup that evening, and by Wednesday I was back where I had started. Well, not quite, because I had stupidly turned off the backup of my iTunes library, so I had to do some extra work to restore it. Don’t Do That.
In the olden days, pre-Leopard, I’d have had a backup, but it would likely have been weeks out of date. Time Machine makes it painless to keep current. If you’re running Leopard, but not Time Machine, go buy an external drive (you’ll find suitable ones for less than $100) and get right with the backup gods.
(A feature request: what I’d really like to do with my iTunes library is to keep a current copy backed up, but let deleted files expire from the backup after so many days. I listen to a lot of audio books, ripped from CD, that take quite a bit of space. Once I’m done with them, I really don’t need a backup.)