I try to just follow "the golden rule" and treat my kids the way I would want to be treated. If I made a mistake at work, would I want my boss to hit me, or scream at me? NO. So just because I know that my boss isn't going to beat me, do I screw up at work just because "I can" NO.
For me, I think that expectations are enough. I don't use spanking or punitive measures with my kids, and yet they are very "well behaved" (they are 5,7, and 9). I do talk about expectations, model the kind of behaviour I expect, and treat them the way I'd like to be treated. If there is a problem, we talk about it.
I do think one of the major keys to this is consistancy though. Just because you are not spending the day dreaming up punishments, or setting time out timers or whatever people do, doesn't mean you just sit back and do nothing. Discipline is teaching. It's a full time job. Sometimes I think gentle discipline is more difficult because it takes more time, creativity and patience than just reaching out and swatting someone or getting some kind of instant gratification by screaming your own frustration at them KWIM?
I think that is how some people end up with "out of control" kids. They know they want to use GD, but then are faced with a tricky behaviour situation, and they don't know what to do, so they do nothing- then that snowballs over time. The kids get out of control, because they don't have any kind of guidlines to follow or the parent hasn't set any expectations, because the parent doesn't even know what thier expectations are. I think parents do need to be in control- not control OVER thier children, but in control of themselves and thier emotions so they can teach thier children how to get along in this world.
Please keep in mind I'm generalizing here. I'm not suggesting that anyone here who is having a tough time with thier kid right now is just being lazy or anything. We've all been there! As someone else mentioned there are a lot of different families out there. For some families what some of us see as "out of control kids" is just fine with them. They want thier kids to do whatever they want, whenever they want, how ever they want. That is thier choice.
But for me, like the OP, I do believe that kids (or at least my kids) need boundarys, expectations, and guidelines and I strongly, strongly believe that those can be communicated w/o punishments.
Gosh I hope that made sense, it's really early