Just found the post, Beta 3 is out (and there was much rejoicing), on Official Blog.
I will hurry to upgrade my MT 4 Unofficial Blog from Beta 2 to Beta 3.
Based on the Official Blog, three new features are added on it.
* New welcome message for new users – to help new users get started more quickly and more easily then ever before
* A fully customizable dashboard – add and remove widgets that are most useful to you, and developers, build your own widgets to share with friends and the community
* Fully integrated Style Catcher support – easily change the look and feel of you blog (don’t worry, we will have a lot more new and modern themes for MT before we release!