Scott Guthrie blogs about the release of the Built-in ASP .NET 2.0 Providers:
Today we released the source code for the built-in ASP.NET 2.0 Membership, Role Management, Site Navigation, Session State, Profile, Web Events, and Web Part Personalization providers (basically all of the built-in providers that ship in the .NET 2.0 Framework Redist). You can download them here, and learn more about the ASP.NET 2.0 Provider Model from this site here.
The source code is released under a permissive license that allows both commercial and non-commercial re-use of the source code, and should be very useful both for people wanting to build their own custom providers (you can take our source and just tweak it if you want), or to better understand/debug our existing ones.
Looks pretty sweet.