Microsoft is pushing a lot of great info out on ASP.NET 2.0 for the imminent November 7th release of VS2005.
Here are some documents that went public recently:
Major Changes for Visual Web Developer 2005 and ASP.NET 2.0 from Whidbey Beta 2 to RTM
Security Practices: ASP.NET 2.0 Security Practices at a Glance
Another resource to be aware of is the Security Wiki on Channel 9. This is where the Patterns & Practices team is working out documents like the ASP.NET 2.0 Security Guide listed above. In addition to ASP.NET 2.0, there are guides for ADO.NET 1.x and .NET 1.x. As this wiki evolves, you will see more .NET 2.0 information appear as well.