No actually, I meant VFR, as in an aircraft that is not necessarily in contact with ATC or even with a transponder. So while in VMC, VFR traffic is a potential hazard to aircraft under IFR. Pilots flying IFR tend to forget to look outside in busy terminal environments, especially when it's VMC. (The only one really, REALLY close near miss I've had was in complete and total IMC, by the way, and that was a visual avoidance manoeuvre.) Yes, you're right about "responsibility" in VMC conditions.