Latest improvements include an artwork grabber, Last.fm integration (artist and album info, events, top tracks and albums, similar artists), sleep timer, some Android Beam stuff, more widgets, more animations to choose from, it claims to be faster and use less memory and includes a few minor UI changes to help match the new branding. That’s all for the Market version.
As far as a release date we know it will be very soon. It’s going to be free, but with ads and an in-app purchase to remove them for $0.99. So, it will be the cheapest, most fully featured music app in the Market.