Tahoma a.k.a. Windows Based Hosting (WBH) 3.0 was released in November and is available for download; so while waiting for the final bits on the Krakatoa release (Hosted Exchange) you can start by looking at the WBH 3.0 solution and the extensive information in the excellent new Documentation Viewer (Although the massive amount of documentation is a bit "scary" at first glance).
Furthermore Microsoft is kicking off a series of Windows Based Hosting Webcasts with the Experts from the Hosting Solutions Unit at Microsoft -
See live demonstrations of technical best practices on the full range of Windows-based Hosting topics, including interactive presentations, product overviews, and question-and-answer sessions. Each Webcast session will be hosted by one of the Windows-based Hosting Solutions program managers discussing how-to technical best practices and thought-provoking business perspectives.
Especially the "Active Directory Guidance for Hosting Service Providers" webcast looks interesting and this time they done something really friendly to us Europeans with 3 timeslots (Based on timezones) for each webcasts (Thanks MS - maybe I'll finally manage to see one of these webcasts ;-)