My buddy Chris over at Movie Marketing Madness has written a comprehensive article about Paramount's marketing campaign (viral and otherwise) for Cloverfield.
It's the complete history of the campaign in one place for you along with his very astute analysis of the hype machine for Cloverfield. He points out the difficulties in promoting a movie without a title (it wasn't officially revealed until mid-December) and the multi-pronged approach they used to build hype and buzz for the movie.
I also give MMM props for posting this analysis before the opening weekend box office numbers come in, which IMHO took some guts but also protects him from accusations of "Monday morning quarterbacking" regarding his conclusions.
It's well worth a read if if the word "hype" has ever made it into any of your conversations about Cloverfield.