I don't remember ever believing in Santa Claus. My family did exchange gifts with "Santa" in the "from" field, but as best I remember I always parsed this as what I might now describe as deference to a cultural norm.
Looking back on it, I think I must have mentally assigned Santa to the same class of myths that held Aesop's Fables or stories about Zeus or Coyote: entertaining stories carrying useful lessons about culture, but not to be taken literally. The children in media that believed in Santa always seemed to belong to idealized worlds, so I didn't figure I was expected to follow suit any more than I would have been expected to, say, come up with wacky schemes to get other people to do my chores.
By the time I'd figured out that it was a live cultural norm, most of my peers had grown out of it.
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.