I have no idea who this came from originally. But If you Google it you will find plenty of people who quote it as well.

There are approximately two billion children (persons under 18) in theworld. However, since Santa does not visit children ofMuslim, Hindu, Jewishor Buddhist (except maybe in Japan) religions, this reduces the workload forChristmas night to 15% of the total, or 378 million (according to thePopulation Reference Bureau). At an average (census) rate of 3.5 childrenper household, that comes to 108 million homes, presuming that there is atleast one good child in each.Santa has about 31 hours of Christmasto work with, thanks to the differenttime zones and the rotation of the earth, assuming he travels east to west(which seems logical). This works out to967.7 visits per second.
This is to say that for each Christian household with a good child, Santahas around 1/1000th of a second to park the sleigh, hop out, jump down thechimney, fill the stockings, distribute the remaining presents under thetree, eat whatever snacks have been left for him, get back up the chimney,jump into the sleigh and get on to the next house.
Assuming that each of these 108 million stops is evenly distributed aroundthe earth (which, of course, we know to be false, but will accept for thepurposes of our calculations), we are now talking about 0.78 miles perhousehold; a total trip of 75.5 million miles, not counting bathroom stopsor breaks.
This means Santa's sleigh is moving at 650 miles per second--3,000 times thespeed of sound. For purposes of comparison, the fastest man-made vehicle,the Ulysses space probe, moves at a poky 27.4 miles per second, and aconventional reindeer can run (at best) 15 miles per hour. The payload ofthe sleigh adds another interesting element.
Assuming that each child gets nothing more than a medium sized Lego set(twopounds), the sleigh is carrying over 500 thousand tons, not counting Santahimself. On land, a conventional reindeer can pull no more than 300 pounds.Even granting that the "flying" reindeer could pull ten times the normalamount, the job can't be done with eight or even nine of them... Santa wouldneed 360,000 of them.
This increases the payload, not counting the weight of the sleigh, another54,000 tons, or roughly seven times the weight of the Queen Elizabeth (theship, not the monarch). 600,000 tons traveling at 650 miles per secondcreates enormous air resistance. This would heat up the reindeer in the samefashion as a spacecraft re-entering the earth's atmosphere. The lead pair ofreindeer would absorb 14.3 quintillion joules of energy per second each. Inshort they would burst into flames almost instantaneously, exposing thereindeer behind them and creating deafening sonic booms in their wake.
The entire reindeer team would be vaporized within 4.26  thousandths of asecond, or right about the time Santa reached the fifth house on his trip.Not that it matters, however, since Santa, as a result of accelerating froma dead stop to 650 m.p.s. in .001 seconds, would be subjected toacceleration forces of 17,500 g's. A 250 pound Santa (which seemsludicrously slim) would be pinned to the back of the sleigh by 4,315,015pounds of force, instantly crushing his bones and organs and reducing him toa quivering blob of pink goo. Therefore, if Santa did exist, he's dead now.