I download trial revit2009. I try render a my project (i designed by revit2008 and  render with nXT).
I see that render of revit 2009 no better than. Revit2009 have some tool good : dimension, easy view 3D. I think revit2009 have not more special !!!!!

You may need to update the materials.
Many RAC 2008 materials show up as default in RAC 2009.
The lights in RAC 2008 don't work in RAC 2009 until you edit the families and reload them into the project.

I've found RAC 2009 renderings vastly superior to RAC 2008 and previous versions. The "Draft" mode admittedly is not that great. The "Best" takes 3 days, but looks photo realistic. Check out the gallery on Revit City:
http://www.revitcity.com/gallery.php