New System.AddIn Namespace in .NET 3.5

Anybody that has built an application that supports AddIns (aka add-in, plug-in, etc) knows that there are many design decisions to make and quite a few subtleties in implementing those decisions in particular when it comes to discovering addins, version resiliency, isolation from the host etc. In NetFx 3.5 (part of "Orcas"), a whole bunch of classes do all this work on your behalf and all you have to do is make simple method calls to configure the behaviour.