Since Panasonic released the first EVIL (Electronic Viewfinder Interchangeable Lens) camera the advantage of these mirror-less cameras has been clear, smaller lighter bodies and lenses. At least that is what some people thought it would mean. With the coming of APS-C sized sensor mirror-less cameras such as the new Sony NEX and Samsung NX10, we've seen that the lenses do still need to be somewhat large, in order to cover the image circle of the sensor. The size of the kit zoom (18-55mm) Sony has developed is no smaller than the Canon 18-55mm IS lens that ships with modern Rebels/XXXD models. So that leaves the advantage of size and weight with the camera body itself.
Sony has done a good job in that area, making the NEX cameras even smaller than the smallest micro 4/3s camera, the Olympus E-PL1. Of course unlike the E-PL1, the NEX cameras do not have a built in flash, but they do come with attachable flash units for when flash is required. That is good news, because in the case of the Olympus E-P1 and E-P2 you had to buy a separate flash unit, and considering the price of those cameras it seemed like a cash grab. Not to mention that a separate flash unit takes away from the small, almost pocketable size of the mirror-less cameras on the market.
So the question is, will the Sony NEX3 and NEX5 set the standard for what a EVIL camera should be like? In some ways yes, in terms of size and image quality, but in terms of the user interface of those cameras, I hope that is not the case. From the early previews that I have seen the interface of the Sony cameras is a slow, jumbled mess that would irritate any photographer who wants to use manual controls and settings. The NEX3 and NEX5 look like the perfect camera for someone who is stepping up from a point and shoot, but doesn't want to deal with the size of a DSLR. Of course the only real size and weight savings can be realized when using one of the fixed focal length primes, such as the Sony 16mm F2.8 that is also a kit option. Once you attach the kit zoom or the 18-200mm lens, that is also set to be released with the NEX cameras, you almost lose any of the advantages offered by such a small camera over an entry level APS-C equipped DSLR. You still have a smaller lighter package thanks to the smaller camera body, but overall there does not seem to be much to gain from such cameras as the NEX line.
Based on what I have seen, I think the NEX line still has a long way to go in order to set the standard for what a EVIL camera should be. We might still have to wait and see if Nikon, Canon or Pentax releases an EVIL camera before the mirror-less cameras really start to take over the higher end segment of the camera market. There is a rumor that Sony is also developing a higher end NEX7 for release this fall, which would be aimed more at photography enthusiasts and pros who want mirror-less cameras. We will have to see what that camera is like, and if it does in fact make the NEX lineup more friendly to photographers who want more control over the photos they take, should the rumor be true.