I installed Movable Type 4 today. My first impression is that the installation is a breeze and that it looks completely different from all previous versions of Movable Type. The administrative console looks a bit like Mephisto. At first glance, it looks like Six Apart has applied what they learned building Vox to Movable Type, which is excellent.
This site is still running Movable Type 3.3, but I’m going to try to create new templates in Movable Type 4 and then migrate the site over. Of course, by the time I’m done with my redesign we’ll probably be testing Movable Type 5.