I know grown women who are obsessed with Twilight.. I guess that shouldn't surprise me since there are so many adults obsessed with Harry Potter, but I have a hard time understanding why they'd be interested in all the teen angst.
I don't want to derail the thread into a discussion about Harry Potter, but I don't think that it's entirely geared toward teens the way that Twilight is. The only Harry Potter book that I honestly think was mainly aimed at children was the first one. After that one, the writing became more serious to serve the older audience that became interested. The fifth book and the ones following it, especially, are much darker, more violent, and more mature. The irony with the last book, in fact, was that J.K. Rowling tried to cram so much action, deep themes, heartfelt emotional scenes, and strong language (I actually chuckled when the word "bitch" was used, so unlike Harry Potter) that the whole thing turned more campy and ridiculous than any other book in the series.
Basically, Harry Potter successfully managed to appeal to many different groups of people. Twilight (both the books and the movies), on the other hand, is making no such effort. It's supposed to appeal to the core group of devoted fangirls, no one else. Why anyone else would ever be attracted to it is beyond me.