I will tolerate improper grammar and spelling in an informal setting, like a message board or chat, but when it comes to things that should have been checked over and over, I do get a little anal.
I don't know when I learned to read, most likely before I started school, but I do know I was reading my mother's People of the Americas books in second grade. (People of the Wolf, People of the River, etc) I could always be found with my nose in a book, even while walking down the hallway to the bathroom, or whereever.
My teachers tolerated it most of the time, although some have gotten upset when I would read instead of listening to them give their lessons. Sometimes they even complained when I read ahead in the textbook.
As for Harry Potter, I found myself suddenly disinterested in the middle of the fourth book and I just stopped reading it. I'll get around to it again, maybe after I read the Song of Fire and Ice for the second time. Harry Potter is interesting, but the language is a bit simplistic for my tastes.