It is simply the end of the current Long Count, and December 22, 2012 will be the beginning of the next Long Count, or cycle in the Mayan calendar. In fact, the Mayans have names for the Long Counts, and the fact that they've named Long Counts beyond this one suggests that this won't be the last. It is significant, however, that we are entering a new cycle in the Mayan calendar.
December 21 is the winter solstice, and in 2012 the Sun on the solstice will be almost perfectly aligned with the plane of the galaxy (the Milky Way galaxy). What is astonishing is how precisely the Mayan calendar was able to pinpoint this alignment of the planets.
According to the Mayans we are entering a new age. What does this mean? We think it may have something to do with the shift towards a more Eastern, or spiritualist, way of life. The Western way of life, and the worship of material goods, progress, and capitalism, has accelerated its way headfirst into battles and wars for hundreds of years. Hopefully, our race will eventually elevate itself to a new era of understanding - one where we find ourselves to be more introspective, and spending our time pondering not only the bigger questions of life - but the smaller ones as well. Spending more quality time with our loved ones, and enjoying the moments. Because we feel there will be many more to come.