So I was weighing up the pros and cons of whether it was worth getting a Sony NEX 16mm f2.8 pancake lens in already having the NEX 18-55mm zoom lens to use, and having conducted a much more thorough round of research on it, this is what I can conclude.

The NEX 16mm f2.8 lens has significantly lower default barrel distortion than the Samsung 16mm f2.4 equivalent on their Mirrorless Compact System (MCS) camera range, and generally it could be said that the 16mm Sony lens on the Sony MCS perform a little better too in some regards. The Samsung lens seems to get relatively positive reviews on technical review sites for what it is where as the Sony NEX 16mm f2.8 lens seems to get a little more stick from technical reviewers, maybe because of what is expected of Sony? Keep in mind that the Sony NEX 16mm f2.8 lens for e-mount MCS camera's is still significantly cheaper at rrp than the 16mm f2.4 for Samsung MCS cameras.

From picture samples it seems that shooting at the widest possible aperture for this lens of f2.8 (wide open) at a macro focal depth with the NEX 16mm f2.8 will bring on some interesting bokeh effect at the boarders and corners, in such a scenario the slight blurring at the corners wouldn't matter anyway as its not noticeable amidst the bokeh effect.

From the samples images it's also the NEX 16mm f2.8 lens is clearly very sharp at the centre but is noticeably a little blurred at the corners when shooting between apertures of f2.8 and f4. Meaning you need to stop down past f4 (the threshold is said to be around f8 for best results) in order to get greater clarity across the entire frame, by which point the light drop off will significantly increase even with the built in software assisted vagnette compensation active. 

The aluminium coated construction of the lens is said to be of high quality whilst having a solid premium feel to it overall. 

The Sony NEX 16mm f2.8 pancake lens also has significantly far less default optical barrel distortion than the Sony NEX 18-55mm f3.5-5-6 zoom lens does at the widest viewing angle of 18mm, but if you're using Photoshop this shouldn't present too much of an issue as there is an auto lens distortion correction profile included with Photoshop for the Sony NEX 18-55mm lens.

If you already have the 18-55mm lens and photshop (and you're not too concerned about the less compact form factor of it) it might not necessarily be worth getting the sel 16mm due to the technical limitations of the NEX 16mm pancake lens and the comparative performance of the 18-55mm lens in terms of sharpness and clarity (in being very similar beyond the slight blurring and chromatic aberration found at the corners on the 16mm f2.8 lens which doesn't happen on the NEX 18-55mm lens), they seem to be quit similar in this regard which is strange considering the 16mm f2.8 pancake is a none zoom prime lens. For still image photography the money could be better put towards other types of more serious camera equipment that would give better physical optical performance if you're thinking of seriously progressing at some point with the same kinds of 16mm viewing angle. (even at 15mm on some zoom lenses for other types of camera's)

But having said that if a more compact lens for general use is a must for your Sony NEX MCS camera with less default optical barrel distortion, then it might be well worth considering.

The sel 16mm f2.8 pancake lens should be ok to use with the NEX-3, 3C, 5, f3, 3N, 5N, 5R, and 6. Essentially all nex camera's that have a 16.1 megapixel rating and under. However it's said that any potential optical flaws become much more pronounced on the 24 megapixel sensor of the NEX-7.

If you're working within a tight budget constraint and are looking for a very sharp wide angle prime lens for taking still images, you might want to consider the Sigma 19mm f2.8 EX DN lens. Its said to be a pancake lens, but when you see it you'll think its anything but. It's nowhere near as compact nor does it have as wide a viewing angle as the Sony 16mm f2.8 E-mount lens, but its been touted as one of the sharpest prime lens for the NEX camera that you can buy for the price. It might also be worth noting that the Sigma lens has also been recently updated and revised with a new set of optics and exterior designs too, which has the slightly different naming convention of the Sigma 19mm f2.8 DN-ART (just DN at the end instead of EX DN). For even better performance on a budget NEX prime lens you might want to consider the Sigma AF 30mm f/2.8 EX DN lens which seems to be getting rave reviews  (or the 30mm f2.8 DN-ART update). Needless to mention that you obviously won't be able to get as much into the frame with the 30mm as you can with the NEX 16mm or Sigma 19 at the same distances. The new updated E-mount ART series of Sigma lenses also see's an additional 60mm f2.8 DN-ART prime lens variant that might be worth looking into. All the mentioned Sigma lenses should glean excellent still frame results on the NEX 7 too.