I was a poor kid at a west coast private school, and thank God it wasn't as nutty as Harvard, but I also dealt with a lot of the same issues that you guys describe.
We had the same sort of "college bubble" going on, which meant that most social events were free or cheap, and that also helped equalize everyone, so that class was not super visible. There were a lot of little cues, though, that everyone was richer than I was: the way they all talked about buying clothes at J. Crew and Anthropologie; the way they could all go out to dinner on a whim, and I was the only one who had to check my budget first; that kind of thing.
Or the time when an older friend of mine was graduating, and she told me that she was nervous because it was going to be the first time in her life that she would have to worry about money. 22 years old and she'd never had to worry about having enough money to do anything that she wanted to do, or to buy anything that she wanted to have. Just so amazingly different from my experience. (By that time, I had started being pretty open about my background, so she realized a minute later what a weird thing that was to say to me - although I hadn't said anything about that; I was too stunned to, really - and we had a good conversation about it.)
Now that all of these friends are living on their own and supporting themselves, I feel that they understand me much better than they used to.
But yeah, being a poor person in a sea of well-off-and-rich people is weird. I pretty much stopped concealing my background by the end of freshman year, but it was always a challenge to talk about class in a way that is productive and helpful, and not make people feel like you're just being like "LOOK AT ME I'M POOR." You just can't respond to most blatant displays of privilege and wealth by saying, "wow, I've never bought a single thing from J. Crew, must be nice to be able to afford it." That's not actually enlightening, just annoying. Pointing out class differences had to be done skillfully and selectively, I found, but in the right context it could make for a good conversation.
@Eric Spiegelman A Harvard grad told me that she hated the reactions that people had to "Harvard" - often, fawning awe or threatened defensiveness - so she was trying to just avoid that conversation without lying outright.