I used to backup to a 1TB drive connected and shared by a TonidoPlug using Time Machine. It was a bit of a pain to set up under Leopard, but it worked well enough over the network. A big advantage here is that Time Machine creates a Sparseimage file to back up to, which means it is trivial to "backup your backup"-- all you have to do is mirror that file somewhere else.
I stopped doing this because it was easier and faster in the long run just to plug in a FireWire800 drive and stop messing around with a somewhat hacky solution that occasionally failed and was pretty slow.