Corner performance of lenses designed for the cropped format can be a very noticeably problematic for those of us who have got used to the enhanced corner performance we get when using full-frame lenses on a cropped-format camera, as I have.
Out of curiosity, I checked out the Imatest results at Photozone for the Sony E-mount 18-200mm, which looks like a very useful lens for the NEX-7.
Photozone used a 16mp NEX-5 for the test, so maximum resolution in the centre should be greater with the NEX-7. Unfortunately, resolution in the corners of the frame is abysmal for this lens. A higher resolution sensor will not change this fact.
Of course, corner resolution is much improved at F8 and F11, as is always the case. My point is, it seems a shame to buy into a new system which requires new lenses that are not on a par with what one already uses.
The 18-55/F3.5-5.6 kit lens for the NEX cameras seems to have better edge and corner performance than the 18-200mm, but still not as good as the Canon equivalent 17-55/F2.8, as tested on the 15mp Canon 50D.
Not only is this Canon lens also designed for the cropped format, and therefore relatively light, it has a constant F2.8 maximum aperture across the whole FL range, in addition to significantly better edge and corner resolution.
Even at F2.8, corner performance is better with the Canon lens than at any apertures with the Sony lens, except at F8. The Sony lens has very marginally better corner resolution at F8 than the Canon lens at F2.8, on average. But only on average. The best corner resolution for the Canon 17-55 at F2.8 is equal to the best corner resolution for the Sony at F8. That is, 2135 'Line Widths per Picture Height' for the Sony at 55mm and F8, as opposed to 2138 LW/PH for the Canon at 24mm and F2.8.
Perhaps it needs to be mentioned again that the NEX-5, in addition to being a more modern camera than the Canon 50D, has a slightly larger sensor (1.5x crop factor as opposed to 1.6x for the Canon), and slightly more pixels. The NEX-5 may also have a slightly weaker AA filter which would explain the slightly higher resolution in the centre of the Sony lens.
Bottom line, I would feel very foolish if I were to order an NEX-7 with 18-55mm kit lens if I later discover that Canon announces a similar design of camera next year, also with 24mp, which I could use with my existing 17-55/F2.8, and which although a slightly heavier lens than the Sony 18-55, is better and faster.
There's a lot to be said for choosing your lenses first, then finding a body to suit.