My experience is distinctly similar.
I observed another curiosity. For much of my time playing the game I've got a larger fraction of 50%s right than of 60%s. I think what's going on is that the 50% cases are ones where I definitely have no idea of the answer and have to fall back on heuristics (have I heard of this person? does the name sound old or recent? etc.) -- and the heuristics work better than I can bring myself to admit they do :-).
Hey rationality friends, I just made this FAQ for the credence calibration game. So if you have people you'd like to introduce to it --- for example, to get them used to thinking of belief strengths as probabilities --- now is a good time :)