I'm not planning on leaving Blosxom any time soon, but if I was to switch (again), I'd move to Wordpress. It's getting to be a great package, with solid plans and active development.
Assuming I ever decide to switch, there is a HOWTO describing how to get posts from Blosxom (individual .txt files in folders) into Wordpress (MySQL). It involves a custom Blosxom flavour that spits out a standard MovableType export file, which can be read by Wordpress (and many other weblog packages, actually).
Always good to have options...
UPDATE: Just did a test install of Wordpress on my TiBook. Took under 5 minutes (most of that was actually downloading the files and figuring out where to put them). Took about that long to configure. And about another 5 minutes to export all 400-odd posts from my Blosxom weblog and import them into Wordpress. It worked very smoothly. The only wrinkle is in the translation of the hierarchical categories. Looks like I'll get to touch each post to verify all proper categories are set. Not rocket science, but will likely take an hour or two if I ever switch. Oh, and comments don't make it through the stargate, but that's not such a bad thing...