Last short post is to catch the attention of the developers out there that are interested in building "extensible applications".
With the .NET Framework 3.5 scheduled to hit the market in Q1 2008 with Visual Studio 2008, you find a technology called CLR Add-ins.
From MSDN Magazine, CLR inside Out, .NET Application Extendibility (http://msdn.microsoft.com/msdnmag/issues/07/02/CLRInsideOut/default.aspx): Our goal in designing this model was to enable dynamic composition of version resilient, isolatable components. Our primary concerns were to ensure the add-in developer experience would not be complicated by the mechanics involved in meeting this goal and to make the host's job as easy as possible.
The really cool thing about it is that it will allow you is to generate AppDomain isolated, pluggable WPF Add-ins. If this tease your interest, do not hesitate to visit the team blog: http://blogs.msdn.com/clraddins/.