I'm not sure when the best time is to ditch the paci, but it took us 3 years with our first child. When he was getting ready to start preschool we wrote a letter to the "paci fairy" and mailed off his pacifiers so she could give them to a new baby that needed them (we mailed it to my parents house). It worked like a charm and we never had any relapses. Our second child really never took to one after the first month or so which was fine with me.
Another mom of a hardcore paci lover here! Neither of my boys had any interest, but my daughter loves hers and is still going strong at 18 months. I'm thinking to try to cut back at age 2, but it's such a good soother that I can see age 3 slowly creeping up on us too :)