I posted on micegg's thread.
My DS1 was about this age when he started to become a real handful - tantrums and pushing other children. I found it really hard to deal with, but found that just trying to tell myself over and over that it's not "aggressive" behaviour per se - I really don't think such little children have any malice in them, or any real understanding of cause and effect.
Hence my decision not to use any sort of naughty step (not really my thing anyway, but might have done it if I thought it would work). I have gone with just ignoring as much as possible, intervening where unavoidable (eg if he actually knocks another child over), very concise language ("No pushing!") and giving attention to the child who has been hit/pushed. And as much good, positive attention as I could give DS1 in the meantime.
This approach was working, until DS2 showed up - but we are persevering, and he has started to improve again (DS2 is 5 months).
I don't know about the learnt behaviour thing - I am not aware of DS1 having learned it in the way you describe, but am sure it's possible, they're little sponges at that age. I think, hard as it is to accept, this is normal toddler behaviour, and I think the most one can do is to mitigate it as much as possible with a calm (very difficult!) and consistent approach.
Sorry, probably no help at all - but you have my sympathies, and you are SO not alone. Good luck!