Fast, at least as reliable as the PC's drives, high capacity, portable, easily upgradable, much less hassle than swapping a hundred or so CD-Rs about with my previous favourite method (Ghost / DriveImage saving whole drives to a CD writer), easily checkable (not much is worse than finding your backup won't restore) and much cheaper than other good methods.
Unfortunately, guess what was the one bit of PC kit to go?
So, buy another one or something else?
I'm tempted by a DVD writer, but that means dealing with 20s of DVD+-R[W] discs.
And while I remember - anyone got a QIC-120 tape drive, the sort that fits to the floppy drive controller? Ancient kit, but these used to be much better than swapping a hundred floppy disks around... until the PC with the drive got nicked from someone else's flat leaving me with some tape cartridges I'd like to access at some point.