Autodesk Labs has released a new Shrinkwrap add-on for Inventor 2009.
Many of us have been waiting a long time for this.  You can make a “shrinkwraped” version of your models, removing any internal faces.  This could be very usefull when either sending a model to a vendor or end user when you don’t want them knowing the internal design, but want them to be able to use your product in a design.  Or in making ”lightweight” versions of your models for 3D printing.  Lightweight versions could also help in rendering when memory limitations become an issue.

http://labs.blogs.com/its_alive_in_the_lab/2008/08/shrinkwrap-add.html

Also check out the demo video on You Tube:

http://www.youtube.com/watch?v=JmqSX25blIs