Good to see that the guys and gals at SixApart have spun out Movable Type 5.1 Beta 1:

The Movable Type 5.1 Beta 1 is now available to download and test. Today begins a 3-month period of beta releases and official quality assurance testing. We plan to release a new beta version every two weeks until the application is stable. Once stable, we will be creating release candidates. And we are hoping to offer a stable build by mid May.

Flip through the slideshow, looks like some exciting stuff is coming.