Moving from Radio to Movable Type

I've seen some discussion on the issues related to changing blog infrastructure from one system to another. In my case, I moved from Radio to Movable Type.

My experience is that is was pretty easy to move the data (no data lock in) but the problem was the urls. Even if you take steps to make sure that the root url doesn't change, the individual post and archive urls will probably change which means that anyone linked to your blog before will stay linked to your old blog and so you will experience a disruption in your traffic.