I basically cleaned off a partition on my firewire drive, did a fresh install there, rebooted and used the automatic transfer function to transfer all my old settings, apps etc. Tried things out for a while from the external HD and then used super duper to clone that partition to my powerbook's internal hard drive. Everything works flawlessly, as though it's my old system. A very snappy upgrade process with absolutely no disruption or unpredicted problems.
Happy. very. Mail will take a little time to get used to though. Spotlight is already an inseparable part of my life. Cool.