I bought a 250 GB external hard drive awhile back and I even bought SuperDuper, which I have to say is one helluva backup tool. But I stopped making regular backups because the hard drive appeared to have died from disuse. I was very upset by this because I'd only really done a couple weeks worth of backups and stopped it once I got my new MacBook.
Then I read somewhere on the Web that the problem might actually be a bad FireWire cable. I had a spare one from my 2G iPod so I gave it a whirl tonight. OMFG! That was the whole problem?! I cannot believe a cable could go bad after less than a year; I certainly didn't have it bent or kinked, which I would expect to cause problems.
[UPDATE (10/29/2007): Remember my saying that SuperDuper is "one helluva backup tool?" Of course you do because it was maybe 100 words ago. The backup went extremely smoothly, taking about an hour and a half for a bootable, complete backup. SD allows you to schedule backups, so I set it up to do it nightly at 2 AM since the iMac never sleeps. Two days later and I'm a nightly-backuper! I can't tell you the peace of mind such regularity brings. We've got about 6,000 photos in iPhoto that we haven't yet uploaded to Flickr, we've got movies that exist only on that computer, and we've got music bought from iTunes Music Store that is irretrievable. (Thanks, Apple, for that lovely issue—somehow you know that we've already bought a song if we try to buy it again but you can't let us download it again. Grr.) Thanks to Super Duper, I don't have to worry that our daughters' births might be lost forever! I'm not quite up to backup snuff as I could be but that's just one more external hard drive away.]