I am thinking about moving back to Movable Type, for some of the following reasons:
They set it free 
I initially moved away from MT around the same time that Six Apart kind of fucked us all over. Now that they’re back into releasing a version under the GPL, it’s worth supporting that.
Kick in the bum
I am sort of blogging more now, I guess. I think having a project to do (getting migrated, etc) will give me more incentive to concentrate on it and make it quality.
Multiple blogs
I know you can run several blogs off one Wordpress install in theory. In practice it is still, in my opinion, kludgey and horrid. A system that can do this properly out of the box is, in principle, a better solution.
The interface is fucking amazing
Seriously. So is WP’s new interface, but MT4’s is hella nice.
More intuitive templating
I’ve never loved Wordpress’ templating the way I loved MT’s. It doesn’t hurt that MT’s template tags are much like Matrix’s design elements.
Less hassle for serving
Not that I have a massive amount of readership to be pushing files to, but in principle it is nicer to write static files when you can.
So, you know. There it is.
One Comment
MT really is yummy. I actually gave it a whirl after reading this and finding out it was open source… hell, you know i could do with a reboot.
It’s easy and fast to install, and that interface is really nice. The only feedback I’d have is that I had some permissions issues installing plugins on my server, but all in all pretty easy to sort out.