from what i understand PBL is just that: problem based. you gather in small groups and are presented with a case (ie. a 53 yo caucasian male presents with x, y and z complaints. so and so tests give positive results, while so and do tests give negative results, etc.) and you must do your own research as a group to figure out what's going wrong, and by doing that you learn how stuff works.
traditional is the standard lectures, etc.
personally i prefer traditional. maybe someone knows more about PBL and traditional and they'll post more info.
pbl advantages: solve more like you would in a work setting, get perspectives you might not get if you only studied alone, see the body as a system, more fun, easier to be engaged in subjectmatter
pbl disadvantages: group work can be extremely ineffective at times, one weak/noncooperative team member can really bring the whole group down, still need to have time to learn the basics on your own so will have to spend a lot of time doing that outside of class
at least that's how i see it. i'm applying for the first time this year. hopefully when i interview i will get a better feeling of how it works and whether or not people like it. right now i'm thinking i'd like to go to a school with some pbl but not a lot of it.