AutoCAD WS allows the viewing, markup, and sharing of DWG files among architects, designers and engineers, as well as non-CAD professionals. AutoCAD WS is available for free on the web, on mobile devices with AutoCAD WS mobile, and as a native desktop Mac App in the Mac App Store.
Autodesk has launched a number of cloud services for subscription customers. What you get as a subscription customers depends on what products you have on subscription and if you have a standard, premium or ultimate suite.
Judging from the growing popularity of viewing drawings through your mobile devices we think you'll be interested in learning about an iPad® app called McDwiff, by third-party developer Austin Silver Software.