I was playing with Rhino Mocks which comes with a .dll and a .xml file (for the Rhino Mocks Intellisense) but couldn't get the Intellisense to work.
You need to put the xml file in the same directory as the dll file and then restart VS.
Then all should be fine.
I did find bits and pieces that lacked Intellisense but I guess that that's a problem with the XML file?
Enjoy!