Perkins+Will Grasshopper Users Group posted a few very useful examples on how to merge Grasshopper with REVIT

http://perkinswillgrasshoppergroup.wordpress.com/?blogsub=confirming#subscribe-blog

Using Massing tools can help you generate complex geometry curtain walls.  In the video link below you will see how easy it is to create a curtain wall from a mass.  I also used the "Cut" tool to modify some of the mass geometry and refresh the curtain wall to update to the new form.

This is useful not only for curtain walls but for anything you can think off.  I use it in conjunction with Mass family, Rhino and 3D autocad.