My gym has a rack for the olympic bars and another one for the "ready made" barbells, ie. barbells with fixed weight.
If I'm the only one in the area, I'll take them directly out of the rack and curl in front of it. Otherwise, I'll put it on the floor a few feet away in order to avoid being 'that guy' who is blocking the rack when others want to access the weights.
Whatever you do, please take a step ot two away from the rack no matter where you decide to do them. Nothing urks me more then someone standing so close to the rack that you cannot get the weights yourself.
not at a gym much, but i always add the plates, even small ones, to the bar on the floor when doing an exercise away from a rack. I do that at home too. Not that i do bb curls but for something like an overhead press i believe there's a benefit to cleaning the weight, even a light one, first in tightening up and getting in the mode needed for the reps.
I'd always curl with db's anyway, never liked being 'fixed' by the bar in curls, though i understand an e-z bar is better.
I did squat rack shrugs for about 20 sets last week(about 30 minutes I took over the power-rack, went heavy though ...just to piss off the two TSB's waiting to use it for curls. These f'n guys sat there and read magazines on the couch until I was done. I had only planned on doing about 4 sets.
The guy using it before me pissed me off, he had the bench in there doing 95 lb bench presses with like 5 minute rest periods ...he was working on that new strength-bulk routine called "impossible".
Little bro's ...get the fuck outta the squat rack, either squat in it or do something really heavy with lots of 45's on the bar. I shouldn't have even been doing shrugs over there(with 405 but still), there was a reason for that ...piss off the TSB's.
My gym has a good number of flat benches. So if no one's in need of doing chest, I'll use the bar on the Flat Bench station and curl straddling the seat (there's a mirrored wall right behind it, so I get to watch my form as well)
People doing shrugs in the rack pisses me off too. The main reason for that is because the only people I ever see doing shrugs are small as hell and they only do them so they can load a shitload of plates on there and think they look cool. Then when they actually do a set, it looks like they are humping the bar and having a seizure at the same time as they jerk it up about 1" using every muscle in their body except their traps.
If you can't deadlift the weight from the floor, you have no business trying to shrug it. If you can shrug more than you deadlift, you are either using shit form or need some serious help cause that's just sad.
Now if the gym is empty and no one is near the squat rack then do whatever the hell you want in there. But if there is even the slightest, most remote chance that someone might want to squat, get the hell out of there. Not everyone is going to come up to you and say, "hey I want to squat". Some people will wait quitely for the 30 min while you do your 20 sets of bar humps.
When doing dumbell curls it is your duty to back up 6" from the db rack, perform your set, then set the dbs back in the rack while keeping your hands on them while you rest between sets. This will effectively piss off anyone trying to retrieve a db within 2 feet of the ones you are using.