According to Anthropologist John Moore from University of Florida, the ideal number for a "space colony" is 160.

The "magic number" of people needed to create a viable population for multi-generational space travel has been calculated by researchers. It is about the size of a small village - 160. But with some social engineering it might even be possible to halve this to 80. For a space trip of 200 years, perhaps eight to 10 generations, his calculations suggest a minimum number of 160 people are needed to maintain a stable population. This would produce around 10 potential marriage partners per person, he says, and if this seems a small number, "think about how many people you dated before you got married". "The decrease in genetic variation is actually quite small and less than found in some successful small populations on Earth," he says. "[Inbreeding] would not be a significant factor as long as the space travellers come home or interact with other humans at the end of the 200 year period."

Sounds to me like the ideal number of participants for a survival colony here on Earth. Either 160 people with 100% survival rate, or 320 people with a 60% survival rate, or.... I think we'll be lucky if any number of people prepare for 2012.

Sources: & Google Answers