How did you put it on your application, though? I think you can list whatever you want in your "activities" section, but you have to be careful about overwrought sincerity in your PS. I personally spent over two months abroad, on three separate trips. There are two missions a year, but I haven't had time to go on any since I returned to undergrad in 2006. I have spent considerable time procuring supplies from companies, filling out paperwork, and recruiting fellow OR personnel for this particular mission. I'm talking about it in my PS because it was honestly my pivotal experience. I didn't want to go into medicine before that. I worked in the OR, and I didn't want the surgeon's life style...plus, many are jaded enough to admonish their kids (and me) to go into business instead. But my experience on the mission was my first exposure to medicine outside of surgery, which is ironic considering it was mostly a procedure-based mission.
Do you really think your experience helped you? Or did you already have a 3.8/30+ MCAT and great ECs/LORs? I have found that most of the traditional students I've met who go on missions are priveleged kids who can afford it, not kids who are selected and funded for their expertise. There's nothing wrong with that, but to me, that's like choosing the kid whose parents could afford Yale or Harvard over the kid who got an equally prestigious slot in a state honors program and volunteered in the local hospital's pediatrics oncology clinic.