In reply to Mikael Elbaek.

Mikael, thanks for the comment. I have views on what impact should be, or at least how to approach talking about it but I don't think there's a need to complete throw out the notion of citation counting. Certainly we shouldn't be using impact factors to judge people but everyone agrees on that.
In terms of whether this has been looked at in detail, I'm not aware of any work like that but it would be very difficult. As you not we don't have any rigorous definition of impact do you'd be asking whether some qualitative and difficult to manage variable was correlating with journal IF or something along those lines. For all it's faults the IF is definitely a number so I'm not sure how you'd even approach that kind of quantitative/qualitative measure. What we do know is that for a given author the number of citations received by papers correlates very poorly with impact factor of journal of publication. So if you accept citations as a measure of impact, which I the they are, just not the measure, then that correlation is already poor. But it's interesting to think about how you might address that question.