I think Santa can teach some really fucked up lessons:
1. Your parents lie to you for multiple years about something completely made up.
2. All the Christmas presents are made by Santa's magical elves so you can ask for anything you want without regard to price, except that poor children do get fewer presents than rich children, but whatever.
3. Someone is watching you all the time.
4. Present-getting is fundamentally conditional.
5. Reasons 3 and 4 are the only reasons to be good.
6. Christmas is about getting presents.
However, I think this is largely down to tone and to what else is going on at Christmas. My brother and I used to put out a mince pie, glass of sherry and a carrot for the reindeer LONG LONG after we had both figured out that Father Christmas didn't exist because it was a fun Christmas tradition. But the "dream" of Father Christmas finally died (after several years of suspicion, at around age ten) when I clocked that he had the exact same handwriting as my mother. I was kind of pissed off at the time that they had "lied" to me for so long, but I think I was just frustrated I hadn't figured it out earlier. I don't think it left any lasting scars. :)
That said, if we have children, we're not going to "do" Father Christmas/Santa. He'll be a story, like Narnia or Harry Potter or the Greek gods and goddesses, and we'll probably tell the story at Christmastime but any presents will be firmly labelled "with love from Mum and Dad". We're really not that into the "magic" of Christmas, though, as I hate the hyped-up thing it has become. I feel like our society has a) devalued the true meaning of Christmas (which IS Jesus, not "family" or "tradition" or whatever, although those things are nice too) and b) made Christmas into such a colossal event that it's like the rest of the year is just about waiting for Christmas or recovering from it. It's no longer about getting together to eat some special food and spend time with the ones you love (let alone remembering the nativity) but rather about needing to have some "perfect magical experience" of things that can "only happen at Christmas time", like being nice to people. WTF?
(/Grinch) :)