I don't have any personal experience with giving up the dummies but laying here with my DD now and her gob-full of dummy I know we will in the future so I'll be trying what our friends did.

Our friends took their DD to a big toy shop and let her pick out a toy, within a reasonable price range. They had spoken to her about it so she knew what was coming. She had all her dummies in her little bag and 'paid' for her new toy with all her dummies. It worked a treat apparently although she did find one random one under a couch or something at home but after a quick suck agreed to throw it in the bin. So to be safe you have to ensure you have ALL of them to hand over

I really like that idea, we'll definitely be adding to our list of things to try