I think being published shows that not only are you competent in laboratory research, but that you've gained a level of expertise in a specific area of science. If you publish in a respectable journal it also signifies that you're capable of being productive once you join the medical profession. Its true that plenty of people do excellent research projects without getting published and others get published with crappy articles, but publications can be indicative of a serious research interest. This is particularly useful for those people who want to go into an MD/PhD program.
A couple of the schools I interviewed with asked for copies of my article, and a few faculty interviewers even read them and asked me specific questions. So, I'd say it'd be worse to get published and then be unable to talk about your work. Like the guys said before, no school will accept a person based solely on their publications unless you do something groundbreaking (pretty unlikely for undergrads).