I've always been torn on the Santa issue. On the one hand, I feel like it's a pointless betrayal of the trust of your children --- if you lie to them about something as silly and trivial as this, what else have you lied to them about, they might think --- but on the other hand, this can be a good basis on which to instill the virtue of skepticism and critical thinking; let them learn on their own that Santa isn't real, and why. They can learn not to absolutely trust anyone or anything. Of course, that can backfire by making them paranoid.
For all the things that I never did
For all the places I never was
For all the people I never stopped
But there was nothing I could do..."