Ah well, I don't think it's just us. From the odd distribution of fandoms in the story signups (http://community.livejournal.com/dvd_commentary/54036.html?style=mine), I think it's probably proliferating virally through people picking it up because their friends are - there's about five times as much Stargate Atlantis as HP or indeed anything else, and the only reason I can think of for that is that it's the organisers' home fandom. Though you undoubtedly know more about this than I do.