Someone just sent me a link to a blog post talking about one of the new features of C# 4.0 that will be included with Visual Studio 2010.  It is regarding covariance and contravariance support within the C# language.  This support has been included since C# 2.0 (and consequently, .NET 2.0).  However, it is currently flawed for delegates and interfaces using generics.  Follow this link to find out more about the proposed improvements for the future version of C#:

http://blogs.msdn.com/charlie/archive/2008/10/28/linq-farm-covariance-and-contravariance-in-visual-studio-2010.aspx