I think my work experience as an EMT has been the most meaningful thing I have done in preparation for medical school. With no other experience do you feel the pressure that comes with being solely responsible for a patient's well-being (great insight to the responsibilities of physician-hood). While this is more intense and stressful than being a "coffee-fetcher" in an er (i've also done this), I think the rewards are far greater and the experience is simply unparalleled. Also, it is really easy to get a job, even during the school year. I worked one shift every other weekend or so and full time in the summers (night shift- still time to play in the day, if you don't mind being sleep deprived)...
Anyways, my opinion is prob. biased, but take it for what it worth.