ASP.NET MVC has an updated release candidate that is built on Orcas SP1. There are minimal other changes to the release candidate besides this dependency.
ASP.NET MVC Release Candidate 2
ASP.NET MVC Release Candidate 2 Release Notes
You can also get access to four more preview chapters for Stephen Walther's MVC book. These preview chapters are a draft version of the book that will be up until the book is published.
Chapter 3: Understanding Controllers
Chapter 4: Understanding Views
Chapter 5: Understanding Models
Chapter 6: Understanding HTML Helpers
The latest information about ASP.NET MVC can be found in the list of supporting technologies.