I spent quite a bit of time last weekend finishing my work this past summer for my WIN-DEV talk on "Hosting Applications in Secure AppDomains". I had only a smattering of second-hand information on CLR Hosting in Whidbey at the time, but I now have more information on the new hosting interfaces, and I will be spending some time in the next few weeks playing with this.
I am truly fascinated with the work the SQL Server/Yukon team and CLR team put into this overhaul for Whidbey (see Chris Brumme's post on Hosting for this great story). Chris emphasizes over and over what was put together would benefit the SQL Server/Yukon team on some specific points, but the CLR team also put a lot of effort into making this more usable and generic for real server applications besides SQL Server/Yukon. From what I am seeing so far, this is definitely true.
As I make some discoveries, and "aha" moments, I will mention it here in my blog. I have mentioned before; one great resource at the moment on CLR Hosting in Whidbey is Dino Viehland's blog (rss). He is currently writing a series on the new fiber support in the Whidebey CLR Hosting Interfaces. All his posts have been excellent!