On the Freakonomics blog, they are playing Prisoner's Dilemma. It's fun to read the answers (so many!).
My thinking is that you don't necessarily use the question to find out what the other person will do but to influence him to do what you want him to do (which is the best result for you). I think you ask him where you should meet him in 6 months and then turn that sucker in! Hypothetically speaking, that is.
And not to get too technical, but I think they should name it "Suspect's Dilemma." I'm just saying.