Since the "big lie" effect on children has come up (understandably), I'm going to summarize my conclusions after years of being involved in these discussions on MDC. I think there are a few aspects of "doing Santa" that increase/decrease the odds of a child feeling really betrayed by their parents:
1) If the parents use Santa as a carrot and stick combo to enforce good behaviour, it seems to increase the odds that their child will feel betrayed upon discovering that Santa was really mom and dad. This makes sense to me, as well, as it takes a simple lie (and I'm actually usually extremely honest with my kids, but I make an exception for Santa, the Tooth Fairy and the Easter Bunny...just as my generally very honest mom did with us) and turns it into a manipulative tactic. People don't like being lied to, but I think most people like being manipulated even less.
2) If the parents don't respect a child's own progress through the Santa myth, the child seems to be more likely to end up feeling betrayed. At some point, children become ready to hear the truth. IMO and ime, when a child starts asking if Santa is real, the answer, "yes, he is" isn't appropriate. Some people handle it with the "no, sweetie, he's not" approach, and some use the "what do you think?" approach. With my two oldest (ds2 still believes in Santa), we went through a year or two of "what do you think?" being answered with "I think he's real", and I left it at that. As soon as my child says "I think you and dad are really Santa", then I admit they're right. I think trying to convince a child over their own doubts and thoughts about it, makes them feel disrespected, and betrayed.
3) Pushing Santa really hard seems to add to the effect. Adding extras - glitter on the floors, bites out of the cookies/carrots/mincemeat tarts, sooty footprints (do people really do this? I can't imagine the mess) is fine, but I think it helps to leave some holes. DD1 put the whole thing together last year. I think one of the reasons she put it all together is that i was out shopping "for Christmas" a lot, and had a lot of packages delivered to the door, and there just weren't enough gifts from me to explain it all. She put it together that there were these really full stockings (I freely admit to being a bit unbalaned on the subject of stockings, and I go waaayyyy overboard), and put two and two together. I think that when parents get into really intricate levels of deception, it adds to a child feeling betrayed and foolish.
Anyway - just my two bits, based on my observations here over the years. I didn't realize how many people felt betrayed over the Santa thing until I came to MDC, but most of the families I knew were pretty laidback in their approach.