Being that I've read nearly 10 in the last 2-3 months I'd calculate that I definitely read more than ten in a year. Right now I'm catching up on a series of Clone Wars era book in the Star Wars universe, but normally I like to alternate genres to keep things interesting. I throw in a full reread of old favorites when I feel like it. I'll be re-reading Deathly Hallows at least once before part one comes out in theaters.
On textbooks: I have a lot of books that were technically textbooks for my classes but are either history-related fiction (like Enemy at the Gates or The Other Boleyn Girl) or a nonfiction/other book that was used in the class (example: Joseph Campbell's The Hero with a Thousand Faces). I also read classic literature out of my old Literature book, which I kept since I'd already bought it and it takes up less space than the individual stories/books. Lastly I have a vast amount of reference books related to Harry Potter, Star Wars, creative writing, and history/culture which I peruse from time to time. But all that's in addition to my casual reading.
Oh and I check out a LOT of young adult/children's books on behalf of my mom who is an assistant librarian. Most of those I read in an hour or two to a day or so, depending on the length. I help them decide if the content is Elementary level.