I've long entertained a dubious regard for the practice of lying to children about the existence of Santa Claus. Parents might claim that it serves to make children's lives more magical and exciting, but as a general rule, children are adequately equipped to create fantasies of their own without their parents' intervention. The two reasons I suspect rest at the bottom line are adherence to tradition, and finding it cute to see one's children believing ridiculous things.
Personally, I considered this to be a rather indecent way to treat one's own children, and have sometimes wondered whether a large proportion of conspiracy theorists owe their origins to the realization that practically all the adults in the country really are conspiring to deceive children for no tangible benefit. However, since I began frequenting this site, I've been exposed to the alternate viewpoint that this realization may be good for developing rationalists, because it provides children with the experience of discovering that they hold beliefs which are wrong and absurd, and that they must reject them.
So, how did the Santa deception affect you personally? How do you think your life might have been different without it? If your parents didn't do it to you, what are your impressions on the experience of not being lied to when most other children are?
Also, I promise to upvote anyone who links to an easy to register for community of conspiracy theorists where they would not be averse to being asked the same question.
I don't think learning the truth really affected my development one way or the other. One day when I was I-don't-remember-how-old, I asked to be told the truth and I was. I do remember that I wasn't very good at maintaining the conspiracy former my younger siblings, and almost let the truth slip a few times---and I'm still not very good at it and have almost let the truth slip to children in my family.
I am wary of whether lying to kids habitually is really as good for them as we rationalize, but the real reason I'm inclined not to spread this myth to my hypothetical children is because I am so uncomfortable with lies myself---I can barely even bring myself to do it for the sake of a surprise party or something innocuous like that. I'd rather tell it as what it is: a fun story, like Cinderella or Harry Potter.