If you try to open a project with VS11 Beta, and get an error complaining about a “missing project subtype”

There is a missing project subtype.
Subtype: '{82b43b9b-a64c-4715-b499-d71e9ca2bd60}' is unsupported by this installation.

It may be that you need to install the SDK too. In my case it was a vbproj being used to generate a vsix.