I’ve just completed migrating this site from Movable Type OS to Melody 1.0 Beta. This not as big a leap as it might sound, as Melody is a community fork of Movable Type. Indeed, the whole process has been a lot smoother than my attempt to upgrade from MT 4 to MT 5 (in which I lost my theme for reasons I couldn’t fathom, and ended up restoring from backups).
I’ve been considering making the move for a while. The final push came when Six Apart, the company that created the software, was sold. I’ve no idea what the newly merged company will do with the open source version of MT, but I’m a lot more comfortable relying on (and, maybe, contributing to) a vibrant open source community. The signs are good that that’s what Melody will have.