Hey guys,
I am a structural steel detailer and lately we have been doing a few jobs using engineer's design models rather than design drawings. It is often pretty hard to get the design modeller's to document the changes they are making to their design models, and I have just come across this tool which allows users to compare old and new models using Navisworks Simulate.
http://revitit.com/blog/?p=297
Comes in pretty handy.