I have taken a great deal of interest in reading the comments on this subject. I must admit I am contemplating getting a vest for my old dog, but, I was thinking for training situations and possibly after the completion of a water run to keep her warm. She already gets rugged but it becomes saturated.
Personally, I wouldn't put a vest on a dog in competition. I am paranoid about my dogs getting hung up as it is, and wouldn't want the added worry of snagging the vest on a retrieve. Whilst I admit our water temperatures do not get to the "ice on top" stage, it is still cold, but as there is a maximum of three retrieves through water that is possible, a chamois, good rub down after the run, then rugging, and, for my oldie, a quick massage to stimulate blood circulation before facing the run, seems to do the trick.
But, for training where the dog may have to enter water several times over, or even sit it out waiting their turn, and have a good chance of getting chilled, I would willingly have a vest on my dog for protection.
Just wonder about the cirrent ruling of not administering anything to a dog, whether a vest, boots or even bandage could be classed as administering. As the word "administer" is originally derived from the Latin "administrare", (to be an aid to), I suppose this could be argued so.
Kerry