I actually only learnt this about a week ago:)
Anthropologists believe that the natural weaning age of a child is about 2 and a half years, which is why so many children are still using bottles etc at this age:)
I agree with you about toddlers running around with dummies, but my friend an OT specialising in sensory intergration also says that by takin a dummy away from a child before they are ready can give it up can also cause other issues. She recommends speicifying it can only be used in bed at sleep/nap time and allowing them to make the decision to give it up (you can facilitate this by suggesting they are big and perhaps they could "sell" their dummy for a toy that they would like)
That said I was totally anti a pacifier before James was born. However he is a very big sucker and cannot self soothe without it. He was using me as a dummy to try get to sleep (I breastfeed) and eventually when he was 3 weeks old I introduced it. He actually hates it, and spits it out constantly, but I have taken to holding it in his mouth which actually (strangely)helps him get to sleep. He much prefers sucking on me:) I only use the dummy when he is overtired and struggling to settle, but have introduced his taglet, which I wrap into his swaddling and place against his fac when I put to sleep. I am now finding that unless he hasnt slept at all, just the taglet on his face s enough to get him to settle. I would say that you can start weanin him of his dummy by introducing another means of self soothing (as per the baby sense book) as soon as now, but this doesnt mean that his sucking reflex has disapeared (James makes sucking motions when he is sleeping even when his mouth is empty).