I actually rarely respond to someone that doesn't post their picture - I understand a certain level of privacy, but it shouldn't be such a big deal IMO. And yes, it is disappointing to say the least if you communicate with someone a little and then get a pic which you find to be completely not attractive.
BUT, if a profile seems interesting otherwise but there is no picture, I'll usually say something like "Hey, would you mind sending a picture? I like to be able to put a face with the words." Or "Hey, would you mind sending a picture? You've seen what I look like, it's only fair that I know who you are too!" Both of those are light and breezy ways of asking for a picture without making it seem accusatory or like you are all about the looks.