I have to admit that I don't "get" the whole hoopla over the Twilight series of books by Stephenie Meyer, but I am also not an 18 year-old girl and that seems to be the audience for her books. I dig Vampires but the main storyline for the series is not something that i find to be of interest.
I do however find their online marketing to be of interest!
There are many, many fan sites and areas devoted to her content, but the "official" sites are where the magic truly lies. If you want to get a guided tour of the sites that are adding to the mystique and the backdrop of the series, check out these bad boys:
Stephenie Meyer's Website
And just for a giggle, search a few times on Google for terms like vampires and twilight and see how many sites pop up! They may lack the broad appeal of Harry Potter, but a phenomenon nonetheless!