We just did it with my 27-month-old son, and we were delighted with the results. I have several friends who used it, and all but one said it took more than three days...but within a week, their kids were virtually potty-trained, and it was maybe three weeks before they were comfortable putting them in underwear all day during their waking hours. (Before that, they were still doing a lot of "naked time," just to reinforce the training.) We're on Week 4, and we're thrilled. My son had a couple accidents the first few days, but after that he started using the potty 95% of the time. In the three weeks following that first week, he's averaged one or two accidents a week--and most times, he's on his way to the potty but just doesn't quite make it there on time.
I think the biggest key (in my opinion) was to not give in to the temptation to put the child back in diapers after a couple accidents. With our son, we had to be firm about "we're not using diapers anymore except for naptime and bedtime," and although he cried for about 45 minutes straight on the second day, that was it--after that, he accepted it and has been very comfortable with it ever since. I think putting them back in diapers for anything other than sleep could be really confusing--one minute you're telling them NOT to go in diapers, and the next minute you're telling them to go in diapers.
Just my two cents. For the record, my son is VERY willful and stubborn (in addition to super sweet and wonderful, of course!), so we thought potty training would be a real battle. But he took to this method beautifully. Every child is different, of course, but I would recommend any interested parent at least give this method a try. It has worked great for everyone I know who has tried it.