My DS loved his dummy. He had avent dummies but only had them either when in bed or in the car. Only in the last 2 months have we got it off him (he's now 29 months).
DD was a different story, she was the most unsettled thing I've ever laid eyes on, and she wouldnt have a bar of the avent ones. At 11 weeks we had a trip to tresillian and they suggested a Happy Baby dummy. She took it and still has it now (6 months).
Having said that, they've both been through stages of waking repeatedly for the dummy, and we would employ a couple of nights of controlled crying and then we'd be back to sleeping well.
For the most part we try to get Erin to go to sleep without it, and she does that most if the time, but if she gets upset, or needs resettling the dummy works well.
I have found that if she stirs during the night, I have to let her get upset before giving her her dummy otherwise she lays there and whinges for ages, but if she gets upset first, she goes straight back to sleep.
Sorry about the novel, but I guess what I'm saying is that they have both positive and negative sides, but in my opinion they are a wonderful tool to help keep baby happy.
Ben 25/10/06 + Erin 10/9/08