All pictures - Sony NEX-7 16-50mm f/2.8 a-mount zoom lens LA-EA2 translucent mirror adapter
First off, this is a very sharp lens. However it is very bulky for the NEX-7, made even worse by the new translucent mirror adapter. However if you are looking for a fast "pro" zoom for the NEX system, this is currently the only alternative. In practice it handles OK, but I'm not sure that I would want to carry it for any distance. In reality, its not a lens I would use for my outdoor work, as the results I can now get with the 18-200mm using the lens profile in Photoshop are excellent. The IS means I can use reasonably small apertures, even hand-held, and since what I usually shoot doesn't move too fast, thats fine.
However the 16-50mm f/2.8 would be an option if you were planning to shoot indoors and needed a fast versatile lens. The 24-70mm f/2.8 lens, and equivalents, has been the workhorse of many pro photographers. Wedding photographers seem to like these. However when I was doing that I preferred two fast primes on separate cameras. Since cameras like the NEX-7 and NEX-5n are perfectly capable of shooting either a wedding, portraits or any other indoor event, this could be an alternative. Its relatively inexpensive, compared with Nikon and Canon equivalents, and would do the job nicely. However it should be borne in mind that the adapter looses about 1/3 to 1/2 a stop of light. Again from a personal perspective I would be more inclined to use the Zeiss 24mm f/1.8 or the 50mm f/1.8 (whenever that turns up!!)
However it was interesting trying the lens on the camera, and it produced some nice images. However another thing to take note of, is that the mirror adapter causes a slight delay on the shutter button. Yes it focuses really quickly, but thats restricted by the time it takes for the shutter to take the picture. The delay is very slightly longer than you get with m4/3.
So not really a camera / lens combination I would recommend, unless that zoom range is just what you need. At some point I guess we will get a native equivalent for the NEX system, which will probably be smaller, lighter and faster. Whether it matches the sharpness of the 16-50mm is unknown obviously, and that is certainly a big plus in its favour.