I agree...when the trailer actually hits its gonna blow all to hell, in a good way. This is deliberate viral marketing.
We've had two trailers...one was a small bit, and the latest, just a bit more. If we look at how the information to Prometheus has come to us, it makes good sense. First a leak of the ComiCon footage in the form of stills...and then, set photos, a steady stream of them until the first clip, and then nearly a full blown trailer. This is entirely on purpose, and I'm betting Fox is absolutely behind this. Ridley was an ad man first, he knows marketing, and Fox knows that they have to sell this film, and sell it well.