I'm going to be somewhat... moderate on this subject, I guess. I don't love the taste or texture of cum, and like a lot of the previous posters have said, it can be downright nasty depending on diet, hydration levels, etc. I don't find anything especially erotic about the semen itself, and I don't think it's sexy drooling all over my (or someone else's) chin, face, etc. I know that's a turn on for some people, but it just doesn't do it for me.
With that said, I prefer to swallow anyway. There are a lot of reasons for it, one of the main ones being that it's more practical. I would much rather swallow than have to clean it off of the bed, use a tissue, spit it out, whatever. Swallowing just takes care of all that in the quickest, neatest way possible. Also, I think it does add to the intimacy of sex a little bit. Another big reason is that the men I've been with seem to love cumming in my mouth rather than having to take it out right at the last minute or whatever, and at that point, I'm doing what I'm doing to give him pleasure. Oral sex for me is all about giving and being able to turn him on and make him feel good, so swallowing is just a part of that. I don't love cum, but what I do love is making the man I'm with completely happy and satisfied, and that turns me on. At that point, it's not about me.
Likewise, if it turned him on to cum on my face or chest or whatever, I'd do it. My preference is to swallow because it makes the most sense to me, but I'm flexible. I like to make my partners happy.