One of the new features we plan on shipping for VS 2010 that I've been heads down on for the past few months is the "Extension Manager". I'll be posting more details about it here over the next several months.
For the meantime, you can hear more about it (and see some very early mockups) in Dr. Tim Wagner's PDC talk. The part about the Extension Manager starts around 50:20. The earlier parts of the talk discuss some of the other new features that we're working on, including the new MEF-based editor extensibility model, the VS Gallery, and a general introduction to VS extensibility.