For what it's worth, there are stories where I've appreciated going in with no knowledge except for some reason to think I'd like it (the movie Hugo 3D is a recent example, for Mieville's Un Lun Dun I just had a reasonable guess about genre).
I think I lost some of the impact of A Deepness in the Sky because I knew what Focus was before I started reading.
I think whether spoilers are harmful varies among works and among readers. (For example, ‘finding out how it ends’ was the only reason why I finished reading Digital Fortress by Dan Brown rather than throwing it in the garbage bin right after the first couple chapters; if I had already known the ending I would likely not have enjoyed it at all (except possibly for laughing at it).)
Here's the new thread for posting quotes, with the usual rules: