A good, fair and accurate review.
I have been shooting a GF1, GH1 and GH2 against a Pentax K5 and my older Nikon D3/D300 systems, and I find one shortcoming that Michael mentioned but didn't stress -- the K5 and the D3 are both virtually miraculous cameras (for a long-time film shooter) when it comes to high ISO. The GH2 is better than film (IMHO) but won't touch the Pentax or Nikon. The K5 is so good -- approaching the D3 -- that I've pretty much given up on Nikon. The Nikon system is just too heavy, and I don't print bigger than 13x19. I agree with Michael that for that sized print, you don't lose anything with m/3, unless you're shooting in dim light. For that, the Pentax is pretty much the answer. It's only slightly bigger (but notably heavier) than the m4/3, and has a really good viewfinder. As with most of the APS-C and FF cameras, the real problem is the lenses, if you want to carry a good selection. They are really bulky, compared to the m4/3 -- and that's the problem with the Sony NEX, in my opinion. It is, as Sony says, "the world's smallest interchangeable lens camera," but the lenses are the same old APS-C size. If you want a good selection, you need a mule. Like Michael, I walk around with a 14-140.
A few days ago, I shot a blues singer on Third Street in Santa Monica, just after sunset, with the GH2 set at ISO 1600, and as I expected, there was quite a bit of noise; but it cleaned up *very* well in Lightroom 3. (You need to download the recent LR3 update to use the GH2.) I'd just gotten the LR3, and I was deeply impressed.
In addition to the fact that you don't lose much with prints of 3x19 and smaller, of course, you also don't lose anything at all on the net.
A note on batteries -- the batteries for the GH2 are not the same as the GF1 and GH1 batteries -- you need a different size. I don't know why. Some people have had trouble getting batteries, but I went to the Panasonic site, went to the "parts" section, put in the part number, and it popped right up. I ordered two batteries, and they were here (in California) in four or five days. But that also means carrying two battery chargers, and, if you're like me, and a little psycho about backups, four battery chargers. The chargers are small. I plan to solve that problem by buying another GH2 (or an updated GF) as soon as they are available. If you want a GH2, it pays to keep your eyes open. I was in Samy's camera, in Pasadena, and some guy who ordered one never came in, and they put it on the shelf. I grabbed it. That was back in December...
I have 3 Panasonic cameras, and find that I can get all three, with a good selection of lenses, extra batteries, chargers, etc., in a small bag that easily fits in the overhead of even the smaller regional jets -- a bag smaller than a typical briefcase.
The 100-300 is a marvel. I also love the flexible LCD - I won't be without one, now, if I can avoid it. I think the m4/3 may be the "new" Leica, much bigger and more flexible than the P&S formats, with "good enough" IQ; just as the Leica didn't quite have the IQ of the large format cameras in the 30s and 40s, but the combination of "good enough" and small size was a winner.
My one thought about Panasonic vs Olympus in m4/3 concerns the IS systems. In the Panasonic, IS is lens-based. Olympus uses sensor-based IS. That means that Olympus lenses can be more compact, I'm told. I don't know much about internal IS,but if it's as good as lens-based IS, and if the lenses are indeed more compact, that might be a consideration in the future.