As soon as I asked if Santa was real (at 5 yr old or so), I got the truth. This made me happy. It may have helped me doubt and later leave the Mormon church at 12 yr old; it at least didn't hurt. I've always enjoyed xmas (minus shopping). I probably would have enjoyed it if I'd never heard a Santa story from my parents, but I do have a fond memory of really believing the cookies+milk would be consumed by Santa (4yr old). They definitely played pretend; they just didn't lie to my face when directly asked.
It's valuable to have at least a few people you really trust in your life; while it would be sad to throw that away in exchange for nothing, a Santa-type fun story (presented without "this is a false story ..." preamble, but readily owned up to) won't do any lasting harm.
There are real difficulties in establishing deep trust. Fun little teases like Santa (if not taken to extreme) are the least of your worries. The hard work is elsewhere.
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.