I'm upgrading to the latest Movable Type version. Everything is not finished yet, I have an issue with a diarrhea of paragraphs tags with pretty random closing and starting, and I haven't figured out where the problem lies between NetNewsWire (which I use for most posts) and MT. I also have to find a way so that the ampersand characters in URLs are turned into their valid "&" entity. NNW apparently does not take care of that.
Those issues prevent this site to validate, and it is not a Good Thing :(.
MT is not for the faint hearted. The documentation is fantastic, as always, but following core and custom changes in the templates are the most difficult part to handle. Anyhow, MT rocks.