So if you're involved with teenage culture at all, you've no doubt seen these books EVERYWHERE. Seriously, I didn't think much of it, until I began to notice it in the youth room ALL the time. I finally realized, it wasn't taking one girl a really really long time to read through the books. There were several girls who were reading it, and sharing copies.
If you have no desire to read the books, but are a parent or hang out with teenagers, and want to know the draw of the book; check out this article. (contains major spoilers) It's a pretty decent summary, with more grace for story-telling than you usually find in a Dobson-inspired publication.
Apparently, it's also a movie slated for release less than a month from now. Probably even just the first, in a series of movies based on the Novels. Who knows, if someone pays my ticket, I might even go see it with a bunch of my teen who are fanatics of it.
It's interesting that, so far at least, I'm not hearing/seeing as much parental upset as we did when Harry Potter first began to be popular. It seems almost embraced by the young teen culture, and their parents, even in the evangelical communities. Based on the article linked above, it does actually stand out from much of today's entertainment in it's decency/regard for sexuality; aside from the fact that it's about vampires.
As in any story that's told, especially for artistic and entertainment purposes, having open conversations with your daughters or sons about the book is encouraged. Heck, you may even want to grab a copy and read it along with your child. The themes of love, eternity, devotion, self-image, and over-all "reason to live/die" can be really good topics of discussion with your teen or pre-teen.
You probably don't wanna leave those subjects for fiction to inform.