@Skull:
I don't know where else to put this, so I guess I'll put it here. I really hope Usopp wont end up fighting Spandam. That would be the lamest thing ever and wouldn't resolve his problem at all. He left the crew because he felt he was weak and just a burden, then Sanji says there are things he can do that no one else can do, and thats why the crew needs him. So how the heck is fighting Spandam something only he can do when Spandam is extremely weak (weaker than other guys Usopp has already beaten in the past), and how the heck would that make him feel like he belongs on the crew? Even Chopper and Nami could beat Spandam. Hes pretty much a joke character, and sugar coating the whole situation and claiming hes being underestimated wouldn't change the fact that theres no reason Usopp could beat him when no one else could at all. I want Usopp to do something awesome to redeem himself, but he deserves far more than something lame like a fight with Spandam.
Also, all that crap about accepting hes weak other people bring up was not the point of his character development. That would of been just pathetic, and honestly I'd rather see him go home than give up his dream and keep going with the straw hats without a reason. The point was for him to realise what he is good at and to accel at it. Fighting Spandam wouldn't show that at all. Just that hes still a weakling who hasn't realised anything who gets the leftover opponent and nothing has changed. No matter how Oda tried to spin it, I'd be severely disappointed of thats all Usopp got with nothing else attached to end all of this great character development (which in this case would be totally wasted).
Good points, all. I think what Sanji was referring to is some other mysterious task that pertains to freeing Robin/escaping/fighting the Buster Call. Franky will probably lay a beatdown on Funkfried, but here's another theory:
If Spandam held Robin hostage, who would be the only one with the precision and distance capabilities to take him out?
Usopp.
End of story.
Franky's gunfire could possibly hit Robin, and the Straw Hats' melee fighters wouldn't be able to get close enough (excluding Luffy, but I think Spandam might have better reflexes than Helmeppo).