Its not often we see an OS being developed so much in public, but the latest build of Windows Mobile 6.5 build 23034 is out on XDA-Developers. Here is some screenshots taken by Shady313 showing the OS in action. The most interesting new feature is that the start bar has finally been made narrower, compensating for the much increased size of the soft keys. Also of note is that the OS clearly skins pretty well.
Read more in this XDA-Developers thread here.