Maybe it's not a good comparison, since it's hardly a king's ransom (compared to what's being proposing) and therefore seems to have attracted mostly "amateurs" and "tinkerers", rather than larger corporates with the cashflow and/or credit line to fund a more serious and aggressive R&D program. (I'm not at all denigrating the efforts of the current X-Prize contestants who are achieving wonders with virtually no resources or funding.) I do like the prize concept, since not one cent is paid until a vehicle is delivered fully tested and operational. This approach would definitely get results. Would this contest be open only to US participants?