It's hard to call what 20th Century Fox is doing to promote Ridley Scott's 'Prometheus' "viral." It's not like they're hiding what they're doing, it's not spreading because people found it accidentally, it didn't get popular without the context of the movie itself, and all the movie sites know about it. So let's call it 'in character.' Here's some posters for the movie which don't directly sell the movie.
What they do sell are some of the ships and tech of the film, and though it's hard to pick the coolest aspect of the trailers, the design work definitely deserves to be lauded. Too long have future-tech felt like a shadow of previous Sci-fi movies, and though much of these designs seem straight out of the 'Alien' film cannon, they've got personality.
They're the sort of stuff that makes model building at home that much fun, and it speaks to Ridley Scott's strengths as a director. He's always been great at having thorough design to his tech, and these posters speak to the level of detail that gets nerds buzzing about the practical realities of Science Fiction. It's also great that - though the film may eventually be rated R - Fox is going all out with their marketing.