Marc asks about export in the next version of WordPress. It’s actually the very first item on the list because it got bumped from 1.5 because of time constraints. The main holdup has been WordPress supports rich data like custom fields and slugs, which users love, but it makes a lossless import and export a pain. Most other blog tools have a WordPress importer already simply because it’s a market leader, so don’t think the export will improve portability much, but it should make a nice way to backup and restore a WP blog.