This has been an interesting thread. I've never been somewhere that did a Secret Santa before. I'm trying to picture it being done in my office and it just wouldn't fly. I mean, people just wouldn't be interested, and you would need someone who was really into it, and really organized, to make sure it all went smoothly. Which obviously happens in some places and leads to fun experiences.
I spend about $10 each Christmas on a gift for the one co-worker I feel closest to, and even then I sometimes struggle with what to get him or if I even want to get anything for him this year and if I do should I include something for his wife, etc.. So I wouldn't think it much fun to be assigned to give a gift to someone else, whom I didn't know as well, possibly with a higher monetary limit/expectation. Would that mean I shouldn't give a gift to that one person I feel closest to? But it's nice to hear that it does work in some places.
I would think a group charity donation would run into some of the same obstacles, though. Can people really opt-out without looking like an uncharitable person? What if someone has a philosophical disagreement with the charity chosen? I mean, I think it's great to donate to charity, but personally I feel uncomfortable doing so publicly and I already have charities I donate to, so I might opt-out of a work scheme for those sort of reasons. But obviously if everyone in the group is simpatico on the idea, there's no problem.