Well, I did actually write a plugin now that can both import from and export to Movable Type's
import format.
It's a little rough around the edges still, but seems to do the job. And the content I tested it with did (more or less) survive the round trip from Geeklog to MT and back to Geeklog.
It currently requires Geeklog 1.4.1, but it should be possible to make it work with 1.4.0 if there's enough demand.
What I'm looking for now are people who could test it with real data (any direction). Anyone interested?
bye, Dirk