I work at Borders and I have people coming in all the time asking if I read any good books lately...
I tell them about Twilight and say "It's a good love story between and human and vampire. I've read the whole series a few times now and each time it gets better."
For some reason, that seems to get most people. I think it's the love story part because most girl/women love to read love stories.
As for my fiancé, I just told him he should read the books, and well with me sitting there reading giving him an almost play by play he gave in a read Twilight right before the movie came out. Then last week, he said to me that he really wants to read New Moon, so now he's going to read them all. I also got his mom to read them, and she got two of her friends to read them, lol.