I thought I'd toss in my two cents since there hasn't been as much said from the macaw side of experience.
I have a 32 year old Blue and Gold macaw.

His name is Picasso

He is loud. He is messy. He is naughty. He is destructive. He is sometimes rude. He needs lots of attention, and lots of room. I shell out thousands of dollars on things to make him happy... toys that he can completely destroy in a couple days, fancy food which he mostly throws on the floor, huge cage, outdoor aviary... stands, perches, vet visits, whatever.
My goodness, he is a chore. But I love him.
Regarding temperament, I can't say if he has changed very much from when he was a baby because I got him when he was 27. I CAN say that he was quite a mean, aggressive bird when I got him, and since I've had him he has gotten a very sweet and cuddly side. He says sweet things to me, gives me kisses, and always wants to cuddle and regurgitate for me. I think it's probably more of a handling issue than a hormone issue regarding behavior. He is only nice for me, though. Anyone else comes near him and he will become aggressive.
Time commitment - as much as possible. Picasso ALWAYS wants to be with me, and will call for me constantly if I have him shut in his cage. Unfortunately, I work in the daytime 2-4 days a week. Leaving such an intelligent, active animal in his cage all day always made me feel miserably guilty. I invested in a 10x5 outdoor aviary in a sheltered patio area, which is where he can spend the afternoon in the summertime if I am "busy" (passively watched over by other members of the family, of course). I also made sure that his cage is far more enormous than most people would say he "needed." That way I can feel content that he has tons of room to move, climb, stretch, flap, and play in the safety of his cage on those days that the weather is bad, or during the winter. I ALWAYS make sure that he spends some time outside of his cage every day, anywhere from 1-8 hours. He likes to sit on his playstand and "help" me cook or eat or read or do things on the computer.
Temperamental and screaming a lot? You betcha. If a stranger drives in, Picasso will scream. If there is company over and noise/excitement in the house, Picasso will scream. When my boyfriend is around, Picasso will scream (very jealous). If he feels ignored or neglected or confused or frustrated or happy or whatever... he will scream. And he is loud. When it's just him and me, however, he practically never screams - it's all cute conversation and sweetness. But when he DOES scream, he is LOUD. Your ears will hurt. You can hear him a mile away. I'm glad I don't have neighbors, because they might complain.
He's quite a beast. But he's MY beast. And he'll keep on being my beast forever.