I bought a Thermaltake USB hard drive cartridge system for work last week after almost losing all my data on my laptop. Techreport has a lengthy writeup which I basically agree with, but a bottom line statement would be, for ~$50 this thing is excellent. I got it and a 500GB drive, partitioned half as OSX journaled file system and half as fat32, then backed up my mac and pc at work, using time machine on the mac and Cobian backup on the pc. Cheap, infinitely extensible, and cleverly designed. Well worth a look if you’re in the market for a backup device.
(stupid product name though)