I think I really started reading YA lit when I was about 17 (when I first picked up Harry Potter and The Princess Diaries). Before then, much of the YA books that I encountered at my school library were of the Go Ask Alice variety, more cautionary tales for teens than enjoyable fiction.
I completely agree. I am addicted, and I actually used to like Adult books more though lately I am having trouble getting into some of them. It almost seems as if young adult books are a more well rounded story.
YA books have gotten more diverse and wide-ranging in the past 10 years. YA lit has gone beyond the YA classics like The Chocolate War by Robert Cormier, A Day No Pigs Would Die by Paul Zindel, Forever by Judy Blume, The Outsiders by S.E. Hinton. . . It's an exciting time to be a YA reader and a middle school literacy specialist!