These cameras are becoming much more popular, they are chosen because they are smaller than conventional dslr cameras but look and feel more like a dslr than a compact camera. Many of these cameras also have inter-changeable lenses, so they are more like dslrs than compacts. Compact cameras have also improved beyond all recognition in the recent years and most offer a range of exposure and control options that you would expect on a dslr, so the question is why do people still opt for a full size dslr.
One of the defining points of a compact camera is their size, it is in the name, to achieve this things have to get smaller and the sensor is much smaller than on a conventional dslr, the sensor size definitely has an impact on quality and the smaller it is whilst retaining the megapixel count generally means poorer quality, especially with reference to noise but also sharpness. These cameras use software to resolve these issues of noise and sharpness but this is a fix for something that is wrong and so not ideal. A guide to this can be seen in the Canon G10/11/12 The G10 offered in excess of 14 megapixels but with the small sensor size the quality, noise, was less than desirable and the subsequent cameras in the range had reduced megapixels such that the G12 now has only 10.4 megapixel. These cameras are at the top of any serious photographers list when looking for a compact, I bought a G10 and if I am honest don’t use it as much as I expected because of the quality, well noise at higher ISO settings. I had mistakenly thought it would give me similar results to my Canon dslr cameras and have been disappointed.
Sensor size then has an impact on quality, the number of pixels crammed onto a sensor also seems to have an impact on quality, I have had 5 different dslr cameras and only when I bought a full frame sensor dslr 5D Mk2 did I realise what it was I missing from film, that intangible thing called quality, almost certainly measureable, not by me of course, but something that looks and feels right. You would be correct in understanding that the software and hardware improvements going into new cameras means that noise and increase in ISO options continues and much of what I say here might eventually be tosh but for now it seems quality does indeed relate to size. In full size dslr cameras there are 3 sensor size options, the previously mentioned full frame sensor as found in most of the the professional level cameras and the others are the APS C and the APS H, this article explains it in detail and this graphic shows the relative sizes. The size of the micro four thirds sensor is about half that of the full frame sensor
So the micro four thirds, there are a number of manufacturers who have embraced this market, the obvious being Panasonic/Lumix, and Olympus, but there are also contributions from Samsung, and Ricoh, this site gives an explanation of the benefits of the system and this suggests the best on the market
Understanding that these cameras are not just full size dslr cameras without a mirror and all the space and weight that takes up is important, the sensor is also smaller than that found in dslr cameras and even with all the wizardry of the most recent software the resulting images cannot be as good as those obtained by a dslr.
You have to eventually make a choice based on quality, convenience, usability and that magpie thing that makes most people want new shiny things. I believe that for people actually interested in photography, wanting to make images that have meaning and impact, quality and functionality a full size dslr is better than a micro four thirds camera even though they are heavier and less convenient but as they say “you makes your choice..”