Sorry Adam et al I will have to respectively disagree. I have had a Nex 5N, I now have a Nex 7 and a Nikon V1. To just say a camera won't be successful due to it's sensor size is misguided to say the least.
Have you actually read the reviews of active professionals using the V1, while the sensor size may be smaller it is technically more advanced with both phase and contrast detection actually on the sensor, there is seriously no comparison with speed of the AF and overall speed of the camera, it leaves the Nex 7 standing. The actual quality of the sensor not just the size plays a major part, the low noise abilities for a "smaller" sensor camera is outstanding and comparable to the M4/3rds. Also the noise it does produce is easily adjusted in LR and far more pleasing to the eye than alot of smeared results from other systems.
Also the colour, metering and white balance is also superior than the Nex and M 4/3'rds system.
My last point is that the lenses themselves are far smaller, the camera itself isn't but comparing the 5n or 7 with the 18-55 Kit lens compared to the V1 there is no contest. My biggest gripe with the Nex system at the moment is the size of the lenses, once you go anything above the 16mm pancake the lens size stops making it a "small camera". Where Nikon got it right is that the lenses are far smaller making the whole system more compact. With the Nex 7 you will get better high ISO shots but unless you are actively doing large prints you won't really see any real difference unless of course you pixel peep on screen!
Most people buying into the mirrorless concept will probably be doing hardly any printing and certainly not large prints ie over 10x8. I think Nikon realised this. Look at the amount of photo hosting sites, the vast majority of people I know upload their pictures to facebook or the popular photo hosting websites, but they only print a very small minority of the pictures they take and these are usually small.
Don't get me wrong I love the Nex 7, however it really depends on what you are using the camera for. For static shots, buildings etc I might use the Nex 7, for street photography, out with the family, wildlife the V1 is perfect with it's super fast and accurate AF. I also find the handling of the camera just as easy to use as the 5N.
Micro 4/3 and NEX will for sure - the rest are also-rans especially the small sensor Nikon and the pinhead sensor Pentax .
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A Problem is only the pessimistic way of looking at a challenge