There is a free technology preview of AutoCAD DWG file viewing and editing made possible from your web browser utilizing a cloud of network computers and technology from Autodesk Labs Project Butterfly. You can easily view, edit, and collaborate with others without installing anything on your machine or those you share with. Just upload your DWG, DXF, JPG, PNG, or even a ZIP archive with external references (Xrefs). On July 1st there were many updates released to this web based Project Butterfly.
Butterfly now has a new and simpler way for sharing and co-editing (and with unlimited participants)
Read more from the Project Butterfly teams blog: http://autodeskbutterfly.files.wordpress.com/
Here are a couple drawings I placed on Butterfly showing the Share abilities and settings.
Vessel Saddle (View and Edit Permissions) Check out the snaps and more.
Aztec/Mayan Calendar (view only permissions)
I was even able to place some geospatial data from a DWG over Google Earth data from within Project Butterfly.
Try Butterfly now!