The impact factor is so successful since it's very simple and its definition reads so reasonable.
I always wondered about what papers do get included in the calculation, and indeed I think that the community should get transparent information on this subject. That is, ISI should explicitly deliver explanations on what papers are included for the calculation of the impact factor of each and every journal.
Even in this case, however, the impact factor remains a poor measure of the importance of an individual paper (while I feel that it could be a pretty good indication of the impact of a journal, provided it's calculated in a fully transparent, homogeneous way).
Thus, the possibility of getting direct community feedback on individual papers is a major plus of the open access 2.0 project.