DS1 - 2 yrs 7 months, ds2 - never taken one. Am firmly of the opinion that you either get rid before a year or after they can talk and you can begin to reason with them a little. Ds1 was and still is, very orally fixated. He was a very sucky baby and took to the dummy big style! Yes it was a royal pain trooping in to replace it in the night before he learnt to find them himself (we took the scattergun approach - 6 or more in the cot at any time!) but it was a major source of comfort and reassurance for him during the day at times.
We stopped when he'd bitten through three in a week. We simply primed him for a few days and said that once the last one was broken there weren't anymore and the shops had run out of them. We also let him put the last one in the bin himself, which was a critical thing I think, as it was something we could remind him that he'd done himself. We had less than two minutes whinging when it came to the first crunch, and nothing at all the next day after a brief reminder that it was broken. Oh yes he says, and that was that.
He still sucks things when he'd frightened or very tired, especially labels on toys - it's his big thing. Sometimes I don't think he's even aware he's doing it. If he passes a toy on the floor he picks it up, gives the label a quick suck, does this weird thing where he pulls it through his teeth, and then wanders on...