When I joined MEF, I was looking at some of the places it could be used. One of the more interesting places it can be used is in Visual Studio to extend the editor. When I found you could extend Intellisense, I spent several hours delving into it's capabilities, and came up with the Intellisets extension, which breaks down the default Intellisense list into categories which you can more easily browse through.

So instead of this for the global Intellisense List:

You get this:

And instead of this list for a DateTime variable:

You get this:

I've written up a walkthrough to help others get started with extending Intellisense, as well as the source code and the actual extension, all of which are attached to this article.