Sarah Miller, Alix Flinn, and A Chair, A Fireplace & A Tea Cozy are all discussing the question of what kind of books a child with "advanced" reading skills should be given.
My feelings on this one are mixed -- I'm never in favor of pushing kids to do things they don't enjoy, but when I was eight years old, I read (and loved) Gone With the Wind, Scarlett, and Nicholas and Alexandra. At the same time, I also devoured Babysitters Club, Cherry Ames, and Sweet Valley Twins books (and tried to sneak in some Sweet Valley High against parental orders -- I wasn't often in trouble, so that incident was pretty memorable).
I'll admit that I didn't get everything in the adult books at the time (the glorification of slavery, for one, along with the phrase "barroom brawl" -- instead of breaking it into "bar room," I put the accent on the second syllable and treated it as a mystery adjective -- and Alexandra Ripley's love scenes went completely over my head).
But I was pretty clear on the plots and characters, and I went around quoting my favorite lines for weeks. A lot of that quoting went into the journal I had to keep for school, so I've always wondered what my third-grade teacher thought of that.