Was just reading on Scott Gu's blog about the release of Visual Studio 2008 and .NET 3.5, and came across an excellent description of the new extension methods feature in .Net 3.5. I have to say that until I saw this blog post, the quick overview from Mike Taulty at TechEd lost me somewhat as to what the purpose of these extension methods is, and also how they apply to LINQ...
http://weblogs.asp.net/scottgu/archive/2007/03/13/new-orcas-language-feature-extension-methods.aspx