Digital Photography Review provides a very in-depth article about what exactly Micro Four Thirds is, but for the everyday photographer who doesn’t understand what flange back distance or the point of sensor size is, this is a brief overview of possible pros and cons of Micro Four Thirds cameras.

Micro Four Thirds System (from dpreview.com)
The fundamental positive of the Micro Four Thirds system is that the cameras can be created with less material. Whether or not smaller camera size itself is a pro or con is determined on a case-by-case basis. For the everyday photographer it is most likely a positive — we love our small digital cameras that fit nicely into our pockets. As more and more soccer moms are on the sidelines with DSLRs, the idea of a compact camera with much more functionality than a point-and-shoot becomes appealing. For travel enthusiasts, especially, a quality alternate to a point-and-shoot could make the Micro system a hot seller. For professional photographers, however, the Micro system could lend itself to a poor user experience with its tiny body.
The Micro Four Thirds system could become the avenue through which everyday point-and-shoot users try out a DSLR-like camera. (Micro Four Thirds is not an SLR, but provides similar functionalities.) For those of us who see DSLRs as cameras for professional photographers, the Micro system’s compact size could be the invitation that we’re looking for.
Another positive for everyday users is that we most likely haven’t invested hundreds or thousands of dollars in camera equipment (yet). If you’ve been content with your compact camera but are possibly looking to explore more avenues of digital photography, the Micro Four Thirds system is most likely the next big thing and has the potential to be a quality investment. For users who have invested in DLSR systems, the Micro Four Thirds system is probably less appealing — it requires purchasing new lenses and possibly changing brand systems altogether if you are loyal to Nikon or Canon, all of which will not work with the DSLR equipment you already own.
Overall, the Micro Four Thirds system looks promising for the everyday photographer. It houses DSLR capabilities in a point-and-shoot size. If you plan to become very involved in photography, however, it might be wise to hold off on purchasing a Micro system. The technology is still very new and nowhere near as established as the DLSR systems that are currently available. Not only will the selection of body styles and lenses be limited for awhile, the number of companies that carry the Micro system will be limited as well. Currently only Panasonic and Olympus are developing the Micro Four Thirds lineup of equipment.