Great article on the Arden Third Edition of the works, which has taken the bold step of publishing *three* different Hamlets (bad quarto, second quarto, and first folio) as separate texts, rather than trying to blend them. The author of the post goes on to discuss how the separate scripts demonstrate that Shakespeare was first and foremost an actor who wrote scripts, and not some poetic genius locked up in a room by himself cranking out lines he never blotted. On the contrary, there's lots and lots and lots of rewrites.
I think the major problem with this theory is that each change between the scripts does not necessarily represent Shakespeare himself saying "Ok, I didn't like that, I'm changing it." There are many other hands at work, including his fellow actors, the typesetters, and so on. For any given change between scripts you can't say which one was what Shakespeare intended.