I would like to know how to implement webservice using ASP.NET AJAX in a n-tier architecture. which one is better n-tier arch or MVC. Where can I download good realtime examples for n-tier architecture?  which is the best design pattern to use in n-tier application?

I've been following the discussion on Phil Haack's blog surrounding how best to introduce polymorphic objects into the MVC framework as part of the framework's interface for developers to work with.  In .NET, there are basically two ways one can build in this polymorphism: interfaces and abstract base classes.  There is a very vocal set ...