Tooth Whitening Products?

DentistsScareMe! asks: "I'll admit it: I've got yellow-stained teeth, and it bugs the hell out of me. I've seen ads (infomercials) over the past few years, but knew them to be mostly hoax products and have steered clear. But now I've noticed the more major (and reputable) pharmaceutical companies jumping into the act, offering their own products. They're moderately expensive ($30-$50), but I'd be willing to foot the large sum _if_ I knew how well they worked. Their ads claim clinical proof, but what exactly does that mean? Did a researcher test the drug on a sample of people to measure effectiveness? Does use of the phrase 'clinically proven' require anything like FDA approval? Has anyone out there used any such product, or know someone who has? Care to comment on how well it has worked?"