I'm trying out an offline blogging client that runs on Linux (these things are not that easy to come by). It's called Drivel, and it seems to work OK, as long as you tell it that your WordPress installation is actually Movable Type.
Oh, and it looks like it only supports one category per post, and no native tags. Not very impressive, really.
(ETA: tags added later via the web interface. Far from satisfactory, really.)
(E further TA: damn, it looks like this theme isn’t showing native WordPress tags, anyway.)