Tad Williams is definitely on my No Thanks list. Dragonbone Chair was lethally boring, and when I tried a few of his other works I couldn't stand them either.
David Eddings *flees*
Other than that, I don't really remember. I just forget books I don't like, which can be a real blessing.
Mostly, I like some works by an author and some not. Jim C. Hines is a good example - some of his books work for me, but there are several where he comes across as pushing his own worldview too strongly, or the characterization get sacrificed for a joke. So I'm wary of books by him until I read reviews.