The latest issue of O Magazine (The Oprah Magazine) contains an article on "Why Weight Watchers Still Works". Even if you're not on WW, it's still worth reading.
Anyway, tucked away on page 218 is a quote from Dr. Michael Dansinger (the show's M.D.). He didn't mention the show, but does give his opinion (based on the findings of a study, which he coauthored, that appeared in the January 2005 issue of the Journal of the American Medical Association (JAMA)) of initial dramatic weight loss, in which he states "More extreme diets - and more extreme results - are exactly the kind of thing certain people need to begin a long-term change".
He does have an excellent point - when you're obese or morbidly obese, it can be VERY motivating to have the reward of a big weight loss - as long as the person keeps in mind that, for the vast majority, a big scale loss on the first week of a diet (as long as one stays ON the regimen of course) is par for the course. Of course most of us are aware that a lot of that loss is water weight...but it's still a nice reward!