i dont think its as unlikley as everyones saying. most of the hulks strength comes from anger, and id say in fights, the thing that makes him angriest is being hit by someone. with spider-mans apility to avoid almost everything and inability to actaully hurt the hulk, the hulk might get fristrated but he will never really tap into that much power.
after a while of swinging around and catching nothing but air, and with not enough anger to give him a power surge i think he will get tired, once he is tired spider-man is resorceful enough to cut off his oxygen (with the amount of muscle working i think that would affect an already fatigued hulk a great deal) and then try and finish it with a very quick unexpected heavy move, like dropping a cement truck on the hulk.
i know the spider-man fan boys really cheapen spiderman as a fighter, and there is no way he could take down the hulk by trying to go head to head with him i think he is one of the heros whos style really allows him to fight some of the higher up characters and not come away that badly. he did take on firelord and win so hes not just some geek in spandex. ill probably cop a bit for this post but i dont think its as far out there as everyone thinks it is.