I saw on the website that the 2012 event sold out in one day, and so this year they're doing a lottery system where you register for $6 (nonrefundable) at any time over the course of several weeks in January and February 2013, and then the participants are randomly chosen from the lot of registrants, to give everyone a fair (but not guaranteed) shot at being able to ride.

Similar to how the last several space shuttle launches worked. In the 90's NASA couldn't even give away all the tickets to view space shuttle launches. Then the last few in 2010 and 2011, there were so many millions of people who wanted to attend (especially the last flight of all three shuttles) that they had to do the lottery system. I was lucky that I got in to see the final launch of the final shuttle Atlantis STS-135.