To answer that question, a very thorough investigation was made by leading scientists and wise men (!) around the world. After several months of hard work, we proudly present the scientific evidence that Santa doesn't exist:
1: No known reindeers can, from what we know, fly-but there are actually 300,000 species of living organisms that has yet not been recognized, and just because most of these organisms are insects and other small bugs, this doesn't mean that there aren't flying reindeers that only Santa has seen...
2: There are two billion children (people under the age of 18) in this world - but since Santa don't seem to care about giving any presents to muslim, hindu, jewish or buddhist children, this number is reduced to only 15% of the total amount of children, which gives us approximately 321 million children. On avarage, there is 3.5 children per household, which gives us 91.8 million homes. To simplify this further, we assume there is at least one good child per household. (You know, you only get gifts if you were a good boy or girl)
Due to different time-zones, and the rotation of Earth, Santa has a 31 hour workday. This is only if he goes in an east-west direction, which seems logical. This adds up to exactly 822.6 visits per second. The conclusion of this is that in 1/1000 of a second, Santa has to park his sleigh, jump out, get down that chimney, fill the socks with presents, put the rest of it under the tree, eat some old food (in the form of cold coffee and half-eaten cookies), get up the chimney, get in the sleigh and fly on to the next home.
If we then assume, that these 91.8 million homes are evenly distributed across the Earth (Which we know is totally wrong, but it gives us easier calculations.), we now talk a travelling distance of 1.26 kilometers per house-hold, which gives us a total of 115 million kilometers in travelling, if we ignore the fact that Santa has to get down once in a while to do those things all living organisms do at least once a day, plus eating and feeding the raindeers etc.
If we take all that into concideration, we can easily calculate that Santa's sleigh travel with a speed of 1000 kilometer's per second, that is, 3000 times the speed of sound. To compare, we can mention that the fastest vehicle ever created by man, the spacemachine Odysseus, travelled with the humble speed of 44.1 km/s. An average raindeer (Not Santa's!) can come up to an impessing 0.0067 km/s.
3: If you take into concideration the weight of the sleigh, something very interesting happens to our calculations. We assume, without loosing too much precision, that every child get a medium LEGO box for christmas. This gives us that Santa's little sleigh would have a non-relativic mass of 321,300 tons. And in that we haven't included Santa's weight, who according to all tales, is kind of heavy.
On land, no regular raindeer can pull more than a 135 kilos. Even if you would allow Santa's raindeers (Hey, they can fly you know!) to pull 10 times as much, it wouldn't be enough with nine or ten raindeers - you would need 214,200 of them. These facts increase the total weight of this convoy to 353,430 tons. Which is, by comparision, the weigth of about 50 Eiffel towers.
4: 321,000 tons of gifts, 214,200 raindeers and a medium sized Santa travelling at the speed of 1000 km/s causes a huge air resistance. The first pair of raindeers will absorbe a heat energy of 14.3 Terajoule. Per second. Each of them. Both of them will instantly turn into plasma, and expose the raindeers behind them. In less than 4.26 thousands of a second, the entire convoy will turn into pure radiation. Besides this, they will cause a bang of sound, killing everything within a radius of 20 kilometers.
That's not really your nice ol' Santa, now is it?
That's not all - Santa's raindeers will consume so much Oxygen that a global lack of air, will rip the lungs out of every person on the planet.
Is THAT your nice Santa? Is that a nice thing to do? Well, Santa won't really enjoy his ride. I'd say it's very hard on him.
The centering force Santa will be exposed to due to the circular shape of the Earth will be approximately 17,500 G. If a rather thin Santa, let's say he weighs 112 kilos, will be subject to a force of 4,315,015 kilos. This is ridiculously much. With that kind of centering force you could press the juice out of a piece of rock.
In conclusion: If Santa was ever stupid enough to deliver gifts on Christmas Eve, he is very, very much dead now.