As of .Net 3.5, we will gain a built-in method for doing plugins in the .Net CLR -- This article explains the basics of plugins and is followed by a second article focusing on the new System.AddIn namespace
Part of a book by Charles Petzold on programming Windows apps with WPF -- includes a link to all the code samples -- which are really great as a learning tool even if you don't have the book.
Apart from a decent article on the new UI stuff in Vista ... this article includes a great tool for playing with the options for Vista's TaskDialog API so you can see what the options are and how they work.
New CLR libraries incladd-in hosting model, which was discussed in the last two editions of CLR Inside OutSupport for the Suite B set of cryptographic algorithms, as specified by the National Security Agency (NSA)Support for big integersA high-performance set collectionSupport for anonymous and named pipesImproved time zone supportLightweight reader/writer lock classesBetter integration with Event Tracing for Windows® (ETW), including ETW provider and ETW trace listener APIs
An early (prerelease) article about Click Once. It's actually a good article with great source code examples so you can understand the various options for ClickOnce including automatic updates.