I've always wondered about playing experienced players for the 4th striker - ala having Voronin or Fowler in the role. Surely the very nature of the job is the sort of thing you want a youthful someone who's willing to give it his all in an attempt to be 3rd/2nd/1st striker. And while Voronin may still have ambitions that way, Fowler never did - not really.
I really like the look of it when Benitez first arrived, and we had Owen, Cisse, Baros, and S-P/Mellor filling the fourth spot. (Granted that would have been an incredibly one dimensional attack, but that's another issue)