most of the drives today come w/ 3 year warranties (the retail versions) so as long as you buy from one of the name brands (ie, WD, maxtor etc), u should be good.
I bought a WD 160 gig external/USB and had more hell than a drunk man on the wrong train. I thought it was just bad, so I exchanged it. Still the same problem. During backup, it would quit talking to the computer. I got on some forums and apparently WD had trouble when they got to the 160 gig size. I took it back and haven't replaced it yet. I am having too much fun now fighting with Dell and Bellsouth on another problem at this point.
I don't use any fancy backup software, I just copy what I want to save directly on the drive or just work using the drive.
I keep all of my MP3's on there.
I use the firewire because I have USB 1.1 and the firewire is faster and the firewire can be daisy chained which is nice. Also the firewire dosen't use up any of the CPU cycles so that helps the load on the system.
I run Windows ME
and have had no trouble with setting up the drives or using them and with the firewire the drive appears to be jsut as fast as the internal drives. Unpacked them, plugged them in, powered them up, booted the system, windows loaded the drivers and VOILAH! got a new drive, no problem even with nasty old WinME.
Got mine at Comp-usa. New egg carries them also but they are currently sold out.The Link
Oh and beware the "just get an enclosure and jam a drive in there and it works" cause it don't always work. So now I got a nice high capacity drive to stick in the next computer that I am going to build and an apparently useless enclosure. (it might be the ME that I am running, when I build my next computer I might try it out with XP media edition and see if that works.