I found a book at the second-hand store called "Folk Remedies of Vermont" printed back in the early 60's. Guess what it recommended for obesity? Apple cider vinegar.
Apparently Vermont herbalists and folk doctors have been pushing it for a century or two for a number of ailments.
Apparently the stuff has been used for it's health benefits for a very, very long time - going back as far as Hippocrates, who used it on his own patients.
Now, I haven't found any exact explanations of why it is considered beneficial for weightloss, but I don't think a couple thousand years of anecdotal evidence as to it's health benefits should be ignored.
It could be that loss of excess weight is just a nice benefit to improved health. It could be that swallowing a couple of tablespoons of vinegar puts you off your feed.
It might simply improve digestion, as the cider recommended (with the "mother") still has live enzymes in it, which in turn might improve absorption and metabolism to some degree.
Personally, I think using a good "real" vinegar on your salad wouldn't hurt - nutritionally, but I don't think I'd be counting on it to drop any real poundage.
On the other hand, my boss's husband just lost about 15 pounds using the damn things, so what do I know?
Fawn