I don't think any one has mentioned this directly in this thread yet, but I only read the last 4 pages of discussion or so, and quickly at that. This idea has bee nthrown around in other threads before. The idea that the Strawhat crew will learn how to use the techniques of CP9. Forgive me, but I do not remember all the names of these techniques, and I am too lazy to look them up. Luffy already learned how to use their speed technique.
From what I read in this thread, people seem to be interpreting this series of lines:
Ussop: Oh so that’s it!!
Nami: what?
Ussop: I know now! I know now!
as Usopp realizing his place in the crew. Seeing that he has his own talents in different areas. At least that is what I got from reading people's responses.
I am interpreting it differently. I think Usopp just discovered how to do the finger bullet thing by watching Jyabura. After all, he made that statement directly after Jyabura had used "Ookami Hajiki (Wolf Bullet)" on Sanji. Now the question is, will he use this technique directly, or modify it for his own means. Usopp is in general not a close quarters combat person right now, and because of this I have arguments for both paths.
Depending on how the technique is done, Usopp may figure out a way to strengthen his slingshot shots. Without knowing how the technique is done, I can't really say how plausible that is. It would have to do something with increasing the speed or strength of his arm.
Now for the other path, Usopp may use the technique directly to give himself some close quarter combat capabilities, and since it is the "finger bullet" it still fits in with his whole sniper character.