System.Collections.Generic.List is a generic collection designed for performance not inheritance and, therefore, does not contain any virtual members. The following generic collections are designed for inheritance and should be exposed instead of System.Collections.Generic.List.
http://msdn.microsoft.com/en-us/library/ms182142(VS.80).aspx
http://blogs.msdn.com/kcwalina/archive/2005/09/26/474010.aspx
http://blogs.msdn.com/kcwalina/archive/2005/09/23/Collections.aspx