I don't recall being particularly fazed by it myself. Then again, I do think that the realisation was a gradual run rather than a sudden 'oh'. I suspect this is because it's not really something you think about in between Christmases. One Christmas it makes sense to you, the next one you've grown up a bit more, your mind has matured and the next time you think about Santa it's obviously false.
My strongest memory of the whole experience was having an argument about it with my classmates (yes, I was that kid). My parents got many angry calls from other parents about my destroying the Santa myth for their kids.
I tend to think that Santa is a beguiling belief to inculcate in your children because it adds to the fantasy of Christmas. Parents remember the 'magic' of it themselves, and somewhat relive it through their children's eyes. Thus someone spoiling it is not only potentially upsetting for the child, but also for the adult, since they've had x years of living it through their children taken away from them.
as a general rule, children are adequately equipped to create fantasies of their own without their parents' intervention.
Kids may not have any shortage of fantasies they come up with on their own, but there's a big difference between a self created fantasy and one everyone else your age around you believes in, and cultural artefacts (books, songs, movies) push at you.
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.