With ds1 I was with him 24/7, co-slept, breast-fed exclusively on demand, carried him around in a sling...and he still had a dummy. He was such a sucky baby (as aloha says, some babies just are) and even when he didn't want to feed any more he still wanted to suck. I think I would have lost the plot if I hadn't had the dummy - as it was I used to go to the toilet with him in the sling because he wouldn't be put down. Actually, even with a dummy I did lose the plot - but that's another story.
Ds2 wasn't at all like ds1 and with him I did use a dummy more for my convenience, I guess. When I had to put him in the pram and take him out because it was time to pick up ds1 from school - popping a dummy in his mouth soothed him and sent him off to sleep more quickly and with less crying than if I hadn't used one.
With ds1 though I believe he really did need something to suck - but not to be fed constantly. Even with a dummy I still did a hell of a lot of pacing up and down, rocking, singing and shushing at all hours of the day and night.
Dummies don't look great in a baby's mouth - if only because they obscure their gorgeous faces, and they look pretty grim in a 4 year old's mouth when they talk 'round' them...but they are bloody useful and no-one should be made to feel guilty for using them (I never did, actually - it's only since discovering MN that I've read such vociferous hatred of them - not this thread, before anyone leaps on me from a great height).