I have to admit, the 25 is looking very special indeed. With the fast focusing G3 it looks like a very versatile package.
I must admit I'm surprised at how good the G3 and the 25mm is. I've been a great fan of m4/3 since its introduction, but I really didn't think it would (could) get to this level. I did some testing yesterday as the weather was dull, and I tried all my m-mount and Nikon prime lenses on the G3 and I just couldn't better the results from the 25mm.
I know that cameras like the G3 and E-P3 have weaker AA filters than the NEX system cameras and that the really spectacular results I'm getting are at low ISO's mainly, but when you take into account that its such a fast lens and that being a 25mm it will have more DOF, there's an advantage here.
The fastest current NEX e-mount lens is F/2.8 and thats a wide-angle. At a "standard lens" focal length there's probably a 2-3 stop advantage over anything that Sony can offer, with fast AF. (Though you can of course use A-Mount lenses via an adapter) So, in many cases, when you have to use ISO 3200 on a NEX you can use ISO 800 or even ISO 400 on a m4/3 camera, with the 25mm. That not only levels the playing field, it tips the balance towards the m4/3 cameras.
Even with the 12mm f/2 you have a one-stop advantage plus when you add in the in-body IS on Olympus cameras (assuming you don't need a fast shutter speed) you have another one or two stops to play with. Also, I put forward the idea in my previous post that m4/3 images tend to be sharper (because of the weaker AA filter) so when you apply some NR to a m4/3 shot, the difference in the noise levels becomes less obvious.
So as far as I'm concerned the high ISO "advantages" of the NEX system are somewhat undermined. I did some of the test shots for my review in the darkest church I know, and I was surprised at the ISO speeds I was using with the 25mm f/1.4. I.E. they were much lower than I would have expected. Consequently I wasn't getting particularly noisy images.
Plus when I was shooting weddings, I would have "fast" Nikon and Canon lenses. f/1.8 and even f/1.2. However I would often be reluctant to use those lenses wide open because the quality took a drop. So often I ended up using them at f/2 or f/2.8. The 25mm PanLeica lens is so good at its maximum aperture (as indeed is the 20mm f/1.7) that I would have no qualms about using it permanently set to f/1.4. And at the same time probably getting the same DOF as I'm getting with the APS-C lenses at f/2.8. Once you move up to full-frame, you have the disadvantage (and I do see it as a disadvantage) of having very limited depth of field. Its difficult enough to get something in focus with a fast lens wide open when you have time, its close to impossible when things (and people) are moving quickly.
These, to me, are the great advantages of "fast" lenses on m4/3 cameras, and only when we get "like for like" and Sony come out with some fast NEX lenses (such as the Zeiss 24mm) will we see if the NEX system moves ahead. But then how big and how heavy will these lenses have to be to cover the APS-C sensor?
I believe that there is a lot of mileage left in m4/3 yet, and a lot more possibilities. The reported 12-35mm and 35-100mm "pro-spec" zooms show just what is possible. Lets assume they are both f/2.8 throughout. The 12-35mm is only slightly bigger than the 14-45mm kit lens (the old one) apparently. Now imagine what that would be like on an APS-C sensor camera. Anyone who has used the zooms on the Samsung NX system will know what I mean.
Also I know Pentax have some small light prime APS-C lenses, but none of them are particularly fast. The fast (35mm) limited lenses are bigger and heavier.
If we want a small, light and high performance system, m4/3 may well continue to be a real alternative to APS-C. Having said that, I have a NEX-7 on order, but then I am planning to use my M-Mount lenses on it!!