I liked today's post by DrugMonkey on authorship. One item that I think is worth considering is that, in complex and multi-author projects, it's actually really hard to allocate credit on a paper by paper basis. That's because credit can't be broken into pieces that precisely fit "First Author", "Senior Author", "Second Author", and "Middle Author".
I have had the good fortune to be involved with some really exceptional co-authors so I can't actually recall a signigicant authorship dispute. But I do think that this highlights the need to rotate people on large projects to do the best to approximate the level of credit that people should get on projects.
But it's not an easy exercise and it gets harder the fewer the number of papers and the more junior the group (as early career researchers are very sensitive to credit allocation when it comes to being evaluated for employment and such things).