Re: Four Thirds vs Full Frame. Pros and cons.
Some full frame sensors are better than others and the same applies to any sensor format. But the latest full frame sensors in Canon and Nikon DSLRs are exceptionally good. Sony's full frame sensor in their older full frame DSLRs are surprisingly noisy but I'm sure the next generation will be much better.
The OM-D E-M5 has a 16MP Sony sensor and it is the best yet for Four Thirds/Micro Four Thirds. Nikon has gone to 36MP with the D800 but I personally feel only a limited number of photographers actually need that resolution and you have to manage massive files, especially if you are shooting in RAW. Nikon's D3200 has 24MP sensor using an APS-C sensor. Nikon's D5100, which is over a year old now, has a 16MP APS-C sensor. The Nikon D800 full frame sensor benchmarks substantially better than the D3200 even though they share the same pixel pitch. The D5100 is slightly better than the newer D3200, which will be down to having a smaller pixel pitch than the D3200, although I think Nikon and Sony have improved their sensor technology since the D5100. The difference between the D3200 and the D800 is large according to DxOMark figures - and this is unexplained. My only suggestion is that the D800 sensor has benefits from additional engineering that the the budget-priced D3200 doesn't get.
But what are we seeing here? If exposed correctly, any of the latest Four Thirds/APS-C/full frame sensor cameras from Sony, Olympus, Panasonic, Nikon, Pentax, Canon, etc., will produce excellent results in the normal ISO working range. The larger the pixel pitch normally means less noise in more extreme conditions and more latitude for post processing. The gap to Four Thirds used to be large but the new Sony Four Thirds sensor has narrowed that gap. There are no DxOMark figures yet, so how much the gap has narrowed I don't know but I do see a substantial improvement in latitude compared with Olympus cameras using the older Panasonic 12MP sensor.
There is no guarantee that a larger sensor means more resolution. The 12MP Olympus E-5, according to reports, can out-resolve the sensor in a 22MP Canon EOS-5D Mark II, for example. Canon seems to use a more aggressive anti-aliasing filter compared to the low power anti-aliasing filter in the 5D Mark II. Nikon even offers the D800E - which has no anti-aliasing filter so you maximised sensor resolution, although increasing the risk of moiré.
To summarise, I think the need for big, heavy, bulky and expensive full frame DSLRs is increasingly specialised. Smaller, lighter and less expensive Four Thirds and APS-C sensor cameras are now more capable than full frame cameras from just a few years ago and are much more easily justifiable in terms of cost/value.