Battles

@Destinyheroknight said:

You forgetting that Luffy wasn't going all out on him

I'd say Luffy did go all out on him. He wasn't fighting for his life but it was probably one of the most serious fights he's ever actually had.  Take a look at how he dealt with Bellamy compared to Usopp, the bullet attack he finished Usopp off with would have been more than enough to one shot someone like Kuro.
 
I feel like Usopp could probably take out everyone aside from the monster trio.
Nami would be fairly easy, he designed her weapon and she's physically weak.
Robin's extra limbs take damage as if they were attached to her. She got pushed back by the army in Alabasta. I imagine her range is limited and Usopp could snipe her from a distance as long as she didn't sneak attack him before the fight starts.
Chopper could be easily tricked, or his heightened sense of smell taken advantage of. The rotten eggs held Luffy back, they'd probably harm Chopper. Monster point is still uncontrollable and I assume moves slow. Usopp should be able to wait it out.
Franky needs cola to fight effectively. Some of Usopp's plants such as the humandrake, devil and impact wolf could lock Franky down, force him to use his cola reserves to fight them off, or destroy his cola outright.
Brooke I'm not really sure, I still don't have a proper feel for how strong he actually is but I could see Usopp winning easily.
 
We've not really seen enough of Usopp to get a feel of how strong he's actually become. I don't think he'd be able to take out any of the monster trio but i'd put him around Water 7 level Sanji.

@Destinyheroknight: Look at it this way, if you're running towards a guy ready to knock him out and he suddenly spits up blood and falls, odds are anyone would be confused and pause for a moment. 
 I agree that at the start he was most likely not going to fight seriously. However Luffy hadn't thrown a single punch at this point. Once he sees Usopp is fighting to win he gets serious.
 Luffy only uses around 4 attacks in the fight, and doesn't pull punches with any of them. Luffy was deadly serious and the Gatling and bazooka would have taken Usopp out if he hadn't stopped them.

@taichokage said:

Ussop is still the second weakest Strawhat. Post time Skip Ussop is probably only around first appearance pre time skip Luffy and that's being nice. He couldn't beat the top 5, or maybe even top 6 (adding Brook) past or present versions one one one let alone all on one. Any version of Luffy, Zoro, Sanji, Franky or Robin could take him out with ease. I don't know exactly how he would fare against pre time skip Chopper, but if the latter chose to go into monster point, then Ussop isn't beating him either. The only one he could ever beat at all is Nami. That goes for current and past versions.

I'd actually put Brooke slightly above Robin and Franky, just slightly. He's seriously under estimated what with all the comedic relief stints he does.