3 minutes isn't really all that bad. I've probably rested for a couple of minutes between sets for exercises that I'm weaker at, so 3 minutes wouldn't be unheard of...but 5+ minutes? on every set? Yeah, I would say that's being inconsiderate. You'd spend 30+ minutes at one machine if you did that. Honestly, sometimes I'm pretty worn out by set 5 and I don't want to half-ass my last set so I'll rest a little extra so I can push through that last set to completion. If it's crowded, I'm a little more mindful and consider the fact that other people might be doing other exercises waiting to use that machine. This may not be for everyone, but I have zero problems going up and asking someone sitting at a machine how much longer they are planning on using it. I know it's the internet and everyone is an anti-social ADD case, but it helps to not be afraid to go up and simply talk to someone...