For my birthday, SolidWorks is releasing a Pro version of eDrawings, and pricing it at $10. This is something that CAD vendors have to to; mobile apps can't all be free.
IMSI/Design began the trend by pricing the better versions of its TurboViewer for $5 and $10. For a while, there was a $20 pricetag, but presumably that was too high for the 99-cent generation. Autodesk is mulling a version of AutoCAD WS that will cost.
So, what do you get for your $10? Dynamically view cross-sections; measure distances; selection filters for faces, edges, vertices, and holes; add markups and save markups with history. By "you" I mean iOS users; access the program from here and pay half-price for the next month. For Android fans, keep waiting.
What you don't get is an MCAD program. Why would I expect that? Well, more than two years ago, SolidWorks V6 was shown running on a variety of platforms, inlcuding on a tablet device.