There have been a few reviews of the Voigtländer 12mm f/5.6 Aspherical Ultra-Wide Heliar, attached to a Sony NEX 7 via an M-mount adapter (here, here and here). (NOTE: This lens is no longer available from Voigtländer. There is however, a new version with a native E-mount here). The biggest problem is the magenta vignetting that occurs with this lens/body combination. I was lucky enough to have been given the Voigtländer 12mm for Christmas and I've always enjoyed shooting with an ultra-wide. I loved my Nikkor 14-24mm - although it was mammoth in size.
Further down is the Lightroom 4.0 correction that can be used to remove the magenta cast. This lens is fun. With such a wide view and generally great depth of field, manual focusing is not an issue. And despite my earlier critical review of the NEX 7, I'm loving the small and light camera bag I get to carry now. Everything's nice and compact, and a lot more discrete than my previous in-your-face DSLR gear.
Here's a screen shot of the correction I apply in Lightroom which takes less than a second...
The setting above dials down the Purple Hue in the Color correction panel - and the magenta cast is gone.