Well, I just finished upgrading my Movable Type to version 2.51. This took a lot more time that the Upgrade document suggests.
After the Upgrade, I needed to upgrade my templates to take advantage of some of the new features, like the search form to the left, and TrackBacks. I don't really understand TrackBacks, but they are enabled.
I also decided to change my style sheet. This is the Clean style sheet that is one of the standard style sheets shipping with MT. I'm not sure I like it, but I really stink at these style things. I'd like to personalize the style a little bit more, but that will take more time and skill than I currently possess.