I have but it was a while ago that I read it...still use the basic principles with my DS though and it works brilliantly. Probably need to re-read it as my DD is just over 2 now.
It focuses on identifying what it terms 'Start' and 'Stop' behaviour. Start behaviour is for when you want them to start something, like start tidying up, start eating your dinner, start getting ready to go out/go to bed etc. Stop behaviour is for stuff you want them to stop, such as aggressive behaviour, whining, shouting, intimidating behaviour, answering back etc. I found the book most helpful with the Stop behaviour and this is where the 1, 2, 3 comes in.
The key points are when dealing with this kind of behaviour is to keep emotion out of it and don't get into discussions or try to reason with them.
So using pp's example above, 1, 2, 3 would work like this:
DC is swinging on chair
"Stop swinging on your chair."
"I never!" and continues to swing on chair
"That's 1 DC. Please don't do it again."
"How can I stop if I wasn't doing anything....
"That's 2 DC"
If you get to 3 and he's still doing it or answering back you give them a consequence. For a young child time out on the naughty step is perfect, for an older child it might be a consequence like going to bed half an hour early, or no TV, or no pocket money or something like that.
It's a good book and worth reading...and it's worked really well with my DS.