Just got this in today so we'll see how it performs. Seems to be a fairly popular lens due to it's backorder status on most websites. Part of the appeal when shooting with the Sony NEX-7 is it's compact size. I wanted an autofocus prime lens and decided to go with the Sigma 30mm F/2.8. Smaller and shorter profile than using an older lens with an adapter in between, and much more lightweight to make the Sony NEX-7 more pocketable for my casual use.
Sigma also offers this tiny lens for a Micro Four Thirds mount and might be easier to pull focus on than some of those Panasonic lenses that seem to rotate forever. It's a decent prime autofocus F/2.8 lens for about $199, check it out at B&H.
Sigma 30mm F/2.8 Prime for Sony E-Mount