i'm kinda wondering how they rest of the strawhats minus luffy, robin, and franky are going to escape from watery death in the flooded tunnel.
usopp hasn't really 'come into his own' as a lot of people have been expecting, yeah he made it possible to save robin but thats about it. also a couple of chapters ago he tried to explain how Kabuto works to sanji and zoro but they wouldn't let him finish..which leads me to believe it is of some importance that will be crucial to the outcome of the arc…
i think it would be cool if he was able to blow their way out of the tunnel with kabuto's awesome power. that would be a good way for usopp to finally feel a sense of importance in the crew, they would have died were it not for him. but a lot of people think that usopp will be crucial in the destruction of the buster call (even though i think luffy has already started doing that with his gear 3 mayhem). as a side note, does anyone see the significance of saul destroying the buster call being a giant, and luffy using his giant gear 3 limbs to possibly destroy this buster call in the process of defeating lucci? not only would it gain him an even higher bounty than just the invasion of enies lobby and the defeat of CP9, but it would be perfect for robin to see that her own nakama can defend against the buster call like saul did so long ago...
so, usopp might save them in the tunnel, and may still use kabuto against the buster call. but i don't think he would try to just explain its use to sanji and zoro for no reason if oda wasn't planning to use it as a major plot point before the end of the arc.