If you are an Android user like me, I highly recommend checking out the new Android app called Image

Just like its big brother, Autodesk Design Review for the PC, it can:

View 

• Open and view 2D and 3D DWF files from your Autodesk Cloud documents account
• Use multi-touch gestures to zoom, pan, and rotate drawings
• View meta data and other details about elements within your technical drawings

Markup 
• Use simple redlining and intuitive mark up tools to communicate changes
• Add text or comments using familiar callouts.

I can spin models created originally in Revit around on my small Droid X phone, zoom to predefined views as well as anywhere on the model, and query the 3D model for information.  Between that and its mark-up capabilities, it could change the way we do design communication.  Also, it doesn’t cost anything if you have an Android enabled device (or a Windows OS). 

Give it a try and let me know what you think of it!