The Vodka Ad and the Ethics of Endorsement

I was listening to Woody Allen's bit "The Vodka Ad" the other day and wondered about the veracity of the hook he uses in that bit. Is it immoral to endorse a product you do not use?

Of course, there is the question of what constitutes endorsement. The obvious case is someone saying I use it and you should too. Should you say those words if you don't use it? Ads for exercise equipment always feature people who are professional trainers and that contraption for three payments of $39.95 are not the reason s/he has those abs. But is there something wrong with that person saying how great of a workout it gives you and leaving the impression that it was? Is it buyer beware -- anyone fooled by such an ad deserves to be scalped?

When a celebrity allows his or her image to be used to market the product as a spokesperson, does that constitute endorsement and do we have the right to infer that the person really does believe in the product and isn't just collecting a paycheck? Surely, just allowing your work to appear in an ad does not constitute endorsement, so we don't think that when MicroSoft used "Start Me Up" in Windows ads that it meant Mick and the boys are pro-P.C., they just licensed use of the song. But how far do you have to go to have some responsibility to believe in the product? Or is there such a line at all?