It appears there’s simply no way to directly convert from iBlog to WordPress. Awkward. iBlog ostensibly has some ability to export the blog, but the relevant menu items are permanently greyed out. Likewise WordPress ostensibly has many plugins for performing HTML import, but they really suck (and also just ignore categories, tags and other metadata, as far as I can tell).
So I had no choice – I had to write my own converter. A quick and very nasty hack in Python; 175 lines and a few hours later, with one false start (WordPress interprets line returns in its XML as essentially <br>s, which is awkward since iBlog hard wraps everything at ~80 columns). But it’s done. Well, mostly… I only pulled in the text, not the multimedia – pictures, mainly. I guess I’ll have to think about how I can fix all those up… thankfully most of my old posts didn’t make use of any additional “attachments”, so it might even be feasible to fix things manually.
I contemplated generating replacement HTML files for all the existing content on MobileMe, with redirects to the new equivalents here… but then I thought, holy crap, that’d be a lot of work. And for something which is going irreversibly dark in four or five months anyway. So to those who have bookmarks, we salute you..