The question was: Do you judge a book by its cover?
My answer: a clear yes and no.
Yes: When I go book-browsing, I judge a book by its cover. That and its title are the only two things you've got to go by when browsing unknown books, and I absolutely base my desire to pick it up and read the back blurb on whether or not the cover appeals to me. Sometimes an intriguing title can make me move past a lousy cover, but that doesn't happen terribly often, and I actually can't think of any specific examples right now.
I receive books for review, so I don't always get to chose the covers there, and some of them are ridiculously tacky. I'll still give it a chance, but sometimes it really goes against my better judgment. I've just received Eternal Hunger which looks really tacky, and Bloody Good by Georgia Evans was almost as bad - that one turned out to be okay entertaining though. Finally there was Seeing Me Naked by Liza Palmer, where the book was actually really great, but the cover was so suggestive that for the first time ever, I actually felt embarrassed reading it while on public transportation! See for yourself....
Of course, there are also covers that are so gorgeous that you (or I, at least) almost want to frame them and enjoy them in all their beauty. For me, some of those are The Thirteenth Tale by Diane Setterfield and The City of Dreaming Books by Walter Moers. Fortunately here the quality of the book fit the quality of the cover :)
No: When I have books recommended to me, I don't stay away from reading them, just because I don't like the cover. And if I have one edition of a book, I don't go out and buy another, just because I discover I prefer that cover. Some of my favourite books have absolutely hideous covers. Cases in point, the below editions of The Blue Castle by L.M. Montgomery and Hitchhiker's Guide to the Galaxy by Douglas Adams. In both these cases I'm able to disregard the extremely ugly covers because I know and love the books so much.
And although I did write above that I judge a book by its cover when I'm browsing books, and probably pass over what may be terrific books because the cover don't catch my eye, neither do I buy books just because of the cover. An intriguing cover isn't enough. It has to be combined with an interesting-sounding back blurb. So I don't judge books that much.