MovableType 5 is available for beta testing from the movabletype.org website. We strongly encourage you to help them test it out if you have the time.
Some of the advancements with this new release are single click theme installation, the adoption of jquery to replace the older js libraries, new permissions and default roles, webpage and blog structure overhaul, more advanced custom fields and many more enhancements.
If you use or plan to use MovableType for any future work, please help them out with the testing to ensure we get the best possible bug-free release we can for the community.
More info is available on their website here: http://www.movabletype.org/2009/09/mt5_beta.html