Some time ago, PhysioProf asserted that journal articles in the biomedical sciences listing two first authors are misrepresenting the reality of the involvement of those authors.
I'm of the opinion that authorship issues are pretty important. It's not just a matter of which scientists get to take credit for the scientific advance a particular paper reports, but also a matter of which scientists are shouldering the responsibility for what that paper communicates (plus being involved in the further discourse between scientists about the pertinent scientific questions, techniques and so forth).
The score-keeping aspect of publishing and getting your name near the top of a list of authors is a reality of the way science is practiced in many academic contexts today. Undoubtedly, the simple-minded approach to evaluating someone's scientific chops (on the basis of the number of first-author publications, or impact factors, or what have you) also encourages a certain amount of gaming of the system.
To the extent that scientific projects are collaborative and that multiple persons have made substantial intellectual contributions to what is reported in the literature, I think the best policy is one of transparency about just what those contributions were. There are journals in which each the contributions of each of the authors on a paper are laid out in detail. Flagging who is responsible for which piece of the research makes it easier for other scientists to direct their questions to the co-author who can best answer their question. As well, in the event of some piece of the project turning out to be ... problematic, there's some sense of who fell down on the job.
Now, within a framework of "explicit authorship" like this, it's not clear to me that it's necessary to have protracted arguments about who is first author, who is second author, who is fifth author, or who is sixth author. All of the authors have made a substantial contribution to the research being reported, and each of those contributions is enumerated. Further, it is not obvious to me that it is prima facie impossible for two of those authors to have made contributions that are equivalent and that are greater than those made of any other individual contributor to the project.
In other words, it might really be the case that two of the authors ought to be counted as co-first authors.
Getting clear on the specific contributions each of the authors made in a particular paper takes away the abstract question of whether such a state of affairs is possible. Thus, it mitigates worries of whether the authorship order is being used to mislead about who did the most (or the best) work and brings the audience back to the task of evaluating the work itself.