Back when I was a little tacker and had just figured out the truth behind Santa Claus, I was angry that I had been decieved by my parents and vowed never to lie to my children, should I ever have any.
Since then, I have decided that I will deliberately lie to my future offspring and continue the the Santa Claus myth. This is not because I want them to experience any magical wonders of childhood, but rather to serve as an important life lesson. They will know first hand what's its like to be a believer, initially rejecting the facts because of the unpleasant cognitive dissonance caused by the the truth. This may help them gain insight and empathy towards others who continue with their religious beliefs, no matter what choices they themselves make.
It also teaches them that their parents, adults and society are not always truthful to them. As Milkman Dan says:
I'll let you in on a little secret, Karen. You see, Milkman Dan, like most adults, lies to kids whenever he feels like it. And, like it or not, there's precious little you can do about it.
They'll still get presents from me, no matter what they believe.