An excellent paper with this title is now published online at Consciousness and Cognition. It is by Joshua Shepard, a graduate student at FSU. The paper is here, but if your institution does not allow you access, you can email Joshua for a copy at jls09k at fsu dot edu
Joshua's experiments suggest (at least) these two interesting results about people's understanding of free will:
1. Free will is strongly connected to consciousness, such that people are likely to attribute free will and responsibility to agents and actions when the agents' conscious processes play a role in action, even in cases where determinism is stipulated; and people are unlikely to attribute FW and MR when unconscious processes are emphasized. And these results seem to wash out differences between descriptions in terms of brain mechanisms vs. psychological processes (and hence probably offer a better explanation for my prior results in terms of that contrast, which is consistent with what I actually think is going on).
2. People are much more likely to attribute FW and MR to agents when they agree with the information described in the scenarios, an important finding that calls out for more research (it's one I've noticed but not analyzed in my experiments). When they disagree with determinstic descriptions, they are more likely to offer incompatibilist responses.
I hope people will check it out and begin some conversations here.