My criteria meant that the obvious (but not necessarily easy) solution, rsync, was ruled out. Folks suggested rsyncX, psync, and Unison, but I was most convinced by the arguments in favor of Chronosync. Chronosync costs money, but it does exactly what I need it to: it gives me all the power and flexibility of rsync, but with a nice, polished GUI.
But Chronosync has one significant limitation: it can only sync two volumes that one can mount locally. All the Chronosync documentation (which is quite thorough, by the way) presumes that you have two locally-mounted volumes, either over a LAN or through FireWire, etc. But, you'll recall I didn't want to haul the PowerBook into the office.
I thought I'd have to drop my 'no CLI' condition and turn to rsync, but then I read this hint on a related but different topic, and found the suggestion from jctull (scroll down a bit) about how to use SSH Tunnel Manager. Thus, the solution to my problem was to do the following:
- Use Tunnel Manager 2.0 to create an ssh tunnel from the PowerBook at home to the iMac at the office.
- Set up Tunnel Manager (following jctull's instructions in the above hint's comments) to forward port 10548 on the powerbook to port 548 (afp) on the iMac.
- Connect to localhost:10548, which mounts the iMac drive as an AFP volume on my PowerBook.
- Launch Chronosync, set up the sync, and go from there!

