I have no clear memories of the Santa deception bar two:
We left a carrot out for the reindeer (along with a beer for Santa, which should have been a dead giveaway, really) and it was only half-eaten the next morning. Having been recently caught lying, I had figured out vaguely that the liar's reaction to false accusations is denial, and the truthful person's reaction is confusion. I wish I could say some spirit of rationality possessed me to check if my parents were lying about Santa, but it was merely me trying to catch my parents in a lie because they had scolded me for lying previously. I remember asking if they didn't like eating raw carrots, expecting denial or confusion, and being surprised when they smiled and owned up to the whole Santa lie.
The other was going to Religious Education at about age 6, hearing about God, applying my Santa-discovering skills, and being frustrated when the RE teacher refused to own up to the lie.
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.