Chris Kunicki--Office developer extraordinaire--blogs about Smart Documents VSTO2 style

VSTO2 makes it super easy to put your custom winforms UI into the Office Task Pane--like 1 line of code easy (repeatedly press Ctrl+F1 while inside of Word or Excel to see the Office Task Pane appear and disappear if you don't know what the Office Task Pane is).  Previously to do a smart document and put stuff into the Office Task Pane you had “..over 20 API method calls you have to implement. These method calls are very hard to manage and the ending results were often very restrictive.”