Interesting post by Matt Hill about the potential of Mango Blog.
I am biased, so I can't give my opinion, but I am happy to see such enthusiasm from the community.
James Harvey has written a plugin that will add a menu item in your blog admin to read documentation on how to create plugins and customize your blog. You can download and read more at James' blog.
Similar to the Twitter plugin by Mark Aplet, Tweet Plugin adds a Twitter feed to your sidebar using jQuery. You can read more and download at Witheringtree blog