Shawn Farkas has posted an excellent summary of the newest features and changes for Security in .NET 2.0 on his blog. He also links to Keith Brown and Dominick Baier for their lists and resources as well. All highly recommended.
I will be presenting the newest security changes in one form or another at several upcoming conferences: New England Code Camp 4, VSLive! Orlando, and Heartland Developers Conference 2005.