Personally (m), one reason I used to hate it was because it made me feel uncertain about my sexuality. I used to think something along the lines of am I really into guys, or do I just want to be into them for some reason?. But the biggest thing that bothered me was worrying I was being unauthentic with others. I already felt like I was being inauthentic (implicitly lying to since small degree) to straight people. Once I came out as bi, and I felt more strongly attracted to women for a day or two, I started feeling like I was lying to my gay friends, too.
It no longer bothers me. Probably because I've been in a relationship with a guy, or because I'm used to it, or because I just care less about what others would think about how I identify. Or maybe even because I've met more bi folks.
Constantly. I read Harry Potter every year (despite any misgivings I have about the author), lately to my kid before putting them down to sleep.
The God of Small Things, LoTR, the Hobbit, Dune, the Foundation series, the Nightrunner series (by Lynn Flewelling), the Left Hand of Darkness. One of my favorite things to do is to reread novels I loved as a child and see if they held up.
Reading a book again, you notice things you've forgotten or missed. And you've changed as a person, so your understanding is different every time.