Head over to the blog post "Riverbed and DWG 2007 file format workaround" and read the comment by Silver Peak on the DWG file format changes and WAN accelerators issue.
"Riverbed is affected by the AutoCAD file format/ISP setting issue more so than rival Silver Peak, and Silver Peak would like the world to know. To be clear, Riverbed will still accelerate AutoCAD DWG files over the WAN, even on a full save, but the data reduction is less than what Silver Peak is able to accomplish." - Infoworld
I'm still wondering how it is with AutoCAD 2009 and verticals like AutoCAD Civil 3D 2009 and there were no word on verticals in the article.