In trying to figure out how to manage some troubleing cat behaviors in our house, without knowing anything else to try, we used the more punitive measures first (i.e. squirt bottles, nose taps, etc.). We found them to ultimately be counter-productive with our fur-babies.
We inadvertently and quickly instilled a water-phobia in one of our cats to the point that, for a while, if a drop of water came her way from anywhere she cowered and thought she was in trouble. She would also tuck tail and run if any kind of spray-bottle was in use anywhere in the house. To make matters worse, it really didn't stop the "bad" behavior. It was pretty sad to watch, because quite often the water that scared her had nothing to do with her at all. We've made some progress recently though; we let her out onto our balcony under strict supervision one day, and when it started to sprinkle, she looked a bit confused, but didn't freak out. It is pretty hard to get a cat to unlearn an averse response to something that you've taught them to fear/dislike (like drops of water). We really wished we had never tried it with her.
As for the nose tapping and our personal experience -- we had already ruled out spray bottles because of our female cat, so we tried little nose bops with our male when he'd take a bite out of one of us. I honestly think it escalated his aggression. Even if the tap was more annoying than painful, it was aggression on our part towards him, which didn't convey the message we really wanted him to get. We later, more successfully, tried shunning him briefly (removing him from the bed, if he was on the bed when he bit, etc.) and then praising him when he was calm again. At least with our cat, he never really seemed to get the causal connection between his behavior and our response until we turned it around and made it positive. We have found it to be much more effective in the long run to catch the cat doing the right thing, and lavish praise on him at that time. When he has let us pet him for a while without biting or scratching, we praise him and give him a treat. A firm "no", prompt removal from the counter or whatever situation he was in when the trouble started, and a few moments without human attention have worked really well to shape his more troublesome behaviors.
Oh, yes -- I should mention that both of our cats went through some rough times and tried some new things (some good, some bad) after our recent move; we didn't ask them if they wanted to move...and they, like the rest of us, need some time to adjust.