I remember me and my husband deciding we were totally against dummies from day one and my mum stayed with us a month after I gave birth and would keep shoving one into my baby's mouth and my husband would run in and whisper, loudly, 'DUMMY IN AGAIN! DUMMY IN AGAIN!' and we would both freak out and I'd have to have a word with my mother.
And jesus, mothers.
However, we quickly came to the conclusion that the dummy made her really happy when she was really unhappy, and then we went totally the other way and my husband sticks it in ALL THE TIME (she's 8.5months now) and my mum is always taking it out.
Annoyingly, the baby can both crawl and loves to pull her dummy out and put it back in, and I keep a couple of spares around in case I need one in a hurry, so she ends up finding one and putting it in all the time. They do look frightfully common, don't they? All my middle class friends have a no-dummy policy and I always have to make shabby excuses for mine constantly sucking away. And then they say things like, 'Oh, it's so clever the way she puts it in!'
Nonetheless, I sucked a dummy until I was THREE! I remember negotiating with my parents about giving it up, and I remember pretending to my friends when they came to visit that it was a doll's dummy - so really, we're talking well into the 3+ age. I really don't want my baby following suit, however in terms of the bad scary things dummies can do, I can say that I have beautifully straight unbraced teeth and learned to talk pretty early, and according to my parents never shut up. I would just take the dummy out to speak.
I am much more scared of thumbs, because you can't take them away, and they do seem to push teeth forward.