We have lots of clients that use them and their dogs still pull.
Honestly I think it comes down to teaching your dog how to walk on a leash properly. They get used to pulling on the collar and feeling the pressure, you want them to be used to feeling no pressure at all. Also I think Liz got a harness for Inara [I could be making this up...] anyway, someone got a harness for their dog so that their dog COULD pull on walks, which I think is great too. Teaching your dog that when they wear the harness they can pull but should be somewhat polite in a collar.
None of the "no pull" harnesses work in my experience. I do think the gentle leader easy walk harness can be somewhat effective:http://www.google.com/products/catalog? ... CFQQ8wIwAQ
But I've still seen dogs that want to pull, pull against these. It's just like dogs that still pull against their gentle leaders. If they are determined to pull, they are going to pull regardless of the gear they are in.