I'm not really for or against the growing debate, but I just think about our calendar and how it's not arbitrary. Maybe arbitrary in when it starts and begins (since time is arbitrary), but not in how long it is considering our calendar is based on a year which is the length of time it takes earth to revolve around the sun 1 time. I would like to think of the Mayan calendar in this way where in its creation they weren't thinking about what day it would end, but rather how long would it be before a new one begins. (Mind you, I don't really know much of anything substantial about Mayans, so I don't know what a "new one" is referring to other than some event that you could relate to as the event we call, a year.) If it happens to fall on 12/12/2012, then that could be arbitrary in the respect that perhaps if they planned this calendar a single day before they did it would then instead end on 12/11/2012, and so on. My point is, whenever the calendar ends, it marks the end of something and the beginning of something else. I think it's along the lines of what Jonesy was talking about, this ends and new one just plops along, so to speak (even if they didn't get around to making a new calendar for it).
Also, I don't believe it's the end of the world. I never have for any of these doomsayer occasions.