Co-Authorship in Philosophy
There's an interesting discussion of co-authorship over on Leiter's blog. (The discussion is primarily about what input counts as 'authorship' and how credit should be divided between authors, rather than how to go about it or whether it's a good idea.)
My own contribution was to suggest that perhaps we should think of the 'authors' credited in a paper as contributors, rather than authors in the traditional sense. This, I think, better captures some of the reasons for which we may think that someone deserves credit, even if they weren't actually involved in the writing of a paper.