Suggested by Simon Thomas:
Have you ever been put off an author’s books after reading a biography of them? Or the reverse – a biography has made you love an author more?
I'd say Ayn Rand is probably my best example of knowing too much about an author. I did a research project on her in Freshman English in college. Her philosophy was too harsh and selfish to me, and I actually really disliked her after writing the paper. I do eventually want to read Atlas Shrugged and The Fountainhead, but I will definitely do so with a skeptical point of view.
Orson Scott Card's views of gay marriage have put me off him as well. We'll see if I decide to read the other Ender books.
Conversely, the more I know about Beverly Cleary, Neil Gaiman, Kurt Vonnegut, and Jon Scieszka, the more I adore them and their works.