I think shouting at newborns is better than shouting at older children. They are not likely to understand/remember.
I'm afraid I'm with fillyjonk here. I can't remember most of the the things I shouted at ds when he was a baby but 'shut the f*k up' and 'go to f**ing sleep' now are the milder ones. Ds did cry an awful lot though.
I shout at ds much less now he is 2.5yrs old as I know he will get upset. As a baby it made no difference whatsoever to him but it did let a bit of tension out for me, even if I did feel bad about doing it.
I now have Enid down as my role model for parenting 'I lifted dd1 quite roughly once'- Oh for that sort of patience - (I'm really not being sarcastic I'm truly envious)
I'm hoping motherhood will help to move me in that direction - I am getting better, hence I'm less likely to shout at my toddler than my baby. With a bit of luck I will have reached a zen-like place of total calm by the time ds is teenager (some chance !)
I do think this really is down to personality - dh has never and I mean NEVER raised his voice to ds . Dh just doesn't lose his rag. Me on the other hand ....