Oh, that's a tricky one! In general, my feeling is that the bigger a conspiracy theory is, the harder it is to prove and thus the less likely it is to be true. So, re: Area 51, etc., I have a hard time with that because it seems like there has to be a whole lot of people--janitorial staff, busboys, cooks, administrative assistants--keeping that place running who have no incentive to keep their mouths shut. The bigger the thing is, the more people it takes, the more likely there is to be leaks. So, personally, I find the most convincing stories are the ones that are the most nebulous, the most vague, the ones that don't really posit a whole worked out theory so much as just some unexplained thing. In The Unidentified, my last book, I tried to do as much of a survey of postwar UFO and alien sightings as I could, and the one that I came back to time and time again without a clear explanation is the Socorro, NM sighting by Lonnie Zamora. Precisely because it was weird and inexplicable....