I can't stand to see 3 or 4 year olds with them either. We started out with the intention of never using one but relaxed our ideal pretty swiftly as an alternative to going insane. We got away with using it sparingly and by the time he was a year old we'd already established a 'night-time only' rule. He was however very dependent on it and would howl the house down if he didn't have it to go to sleep with, or if he dropped it out of the cot during the night.
We then hit upon a great ruse to phase it out completely. As he was coming up to his rite of passage out of a cot and into a real bed at around 2yrs old we started trailing this idea - that he was a big boy now - that he'd soon be getting a big bed, which was very exciting and - by the way - dummies aren't allowed in big beds. We repeating this over a period of a few weeks and he seemed to be fairly accepting of it. Even then we thought it was still a long shot but come the big day on his first night on the new bed it worked like a dream, and he has never had a dummy in his mouth from that day to this.
This may not work on any other child but I offer it an an idea.
Or failing that you could always douse the teat in vinegar
