Well, I fixed them, the permalinks. A permalink of course is a URL that points to a specific blog entry even after the entry has passed from the front page into the blog archives, or — in my case — to a completely different system. Because a permalink remains unchanged indefinitely, it is less susceptible to link rot. I found that there was a way to accomplish all this more or less automatically, but by that time I had already started on my manual route, so I just continued. By dumping the relevant fields of the MovabaleType database and the WordPress database, it was easy to match the titles in both sets through a small script, retrieve the the old and the new posting IDs and generate a .htaccess ready 301 redirect clause.
Now your old bookmarks will work again, the internal links to previous articles should work too, and not totally unimportant, the old links that Google and other search engines have indexed will now lead to the correct postings.