I dunno, maybe Im overestimating Diaz like some have mentioned here, but something tells me he can bother GSP. Bothering him and beating him are two different things, but I'm still not totally convinced GSP's chin is legit. His KO loss to Serra was eon's ago, but if he starts taking some punches and isnt able to bust Nick up enough to sap him or keep him at bay, he might get roughed up a bit. Eventhen he will still probably pull out a decision, because he is GSP, but I can definitely see Diaz leaving the fight looking the better man (face wise and damage wise).
It would be interesting to see them on the ground but I doubt it happens. Diaz BJJ is a debated topic as some feel its over-rated but Im pretty sure he is good enough to neutralize almost any WW in the UFC. Ill admit Im biased towards DIaz but I would like to see a Jackson fighter, GSP especially, take some fucking chances and give the fans blood and excitement.