There's a great post over on Radio Free Blogistan about his experiences moving blogs between different blogging systems. I wanted to make note of it since he mentions similar issues with Movable Type to what I posted yesterday.

The big problem is converting the backed up entries to the MT format without breaking permalinks. Also, Radio stores each day as YYYY/MM/DD.html whereas MT by default puts each entry on its own archive page, with my preferred URL being YYYY/MM/DD/entry_title.html. In order not to break old links to the site, I'll probably end up keeping a duplicate set of all past entries. That may be confusing to some, but it should minimize breakage. [Radio Free Blogistan]

Once you start moving things between different blogging systems you run into a whole bunch of other issues. Since many of the systems seem to use numbers by default to indicate blog post. One thing that might be useful is for them to start having a seperate field in their internal database for permalink. This way when you import posts you can do so and not worry about any other issues.