A while ago I released two articles about implementing plugins in your .net applications(here and here). I then went ahead and created a generic piece of code that encapsulates the functionality demonstrated in those articles that can be "dropped in" your application to give instant plugin recognition abilities (after small interface modifications). I called it the "Extensibility Application Block" (I then gave it the acronym of "EAP". Don't ask me why, I have no good answer).
I was sure no one was using it, but I was wrong.
Chris Frazier used my Extensibility application block in his most excellent "PostXING" blogging client (which I am using to write this) and gives a nice review of what he had to do to make plugins work for his application. That's pretty cool!
I also learned from that article that RSS Bandit uses the same search semantics explained in my MSDN article about searching for plugins. That's pretty cool too!