I've been a fan for 3 years now. I'd say I'm quite loyal. Even though I don't usually buy her singles or remixes, I make it a point to have every studio album and I listen to her songs a lot. She's the only Jpop artiste I really listen to, except for the occasional Utada and Namie.
Even if, as some of you have pointed out, her music isn't as unique as it used to be, I still love it. There's a kind of Ayu quality that's very personal, and it's not only the lyrics. I don't like certain songs much, but I still can enjoy them if I'm in the mood.
Also, I like to listen to Ayu when I'm studying
It gives me a sense of support. She's so sincere about her music and puts so much effort into her work, it gives me motivation and helps me to not feel nervous for upcoming tests and such.
Oh, and not to forget her fashion! I guess she's taught me to like girly things a little more and has opened up my mind on dressing. Her clothes nowadays are stuff that we folks can't really wear, but it still inspires me.