My master plan to solve this issue:

I presently have my data stored on a LaCie 2x750GB Firewire external drive. I have a second one that I use as a Time Machine backup.

The new hard drives, striped together and running inside my new Mac Pro, will be my primary storage. One of the Firewire boxes will be the Time Machine backup. The other Firewire box will be moving to my office and connected to my work machine, and I'll set up rsync, giving me offsite, networked backups. I figure that, by doing the initial dump while it's still at home, the incrementals shouldn't completely destroy my DSL line.

After Apple releases OS X 10.6, I hope to rearrange the Mac's internal drives to use ZFS. At that point, I can retire the Time Machine drive.