When I used to interview people for a job, I occasionally checked myspace if I thought twice about somebody. Sometimes I didn't like what I saw, for whatever reason. If I had doubts in any way, I usually just skipped over them for the hire because there were plenty more people for the position. Many who interview are taught that such sites are a tool, because people post stuff about themselves on the sites that they would never speak of at an interview. Granted, I was not interviewing for a medical school. But the same principles apply to all interviews.
Facebook and myspace profiles can be locked to users other than your friends. Just be smart and LOCK THEM. Then regardless of what you have on there you can rest assured that the admissions staff cannot see it.
And I have also heard at several of my interviews, from admissions staff, that many of them actually do read SDN. Probably not necessarily prowling for any one particular person, but still, as a rule of thumb don't do anything that is so flagrant and un-anonymous that it could hurt you.
