The difficulty in answering your question is that none of us have been in medical school using both PBL and traditional didactic lectures. Thus I cannot compare my experience with PBL to a traditional curriculum. At the same time I cannot compare my experience with PBL to that at any other school, so what I'll write is only MY experience at MY school.
I found PBL: terribly inefficient and ineffective in teaching the basic sciences. The focus on clinical medicine did not leave enough room for detailed, rigorous investigation of the principles of basic science. The process of learning PBL was frustrating and many in the group did no t participate until forced to do so (by the tutor who felt he could not grade them). I cluld have easily taken the cases home and used them for my own framework for studying and done without the biweekly PBL sessions - they were just *very* little help to my understanding of the case.
PBL was effective and a more interesting way to learn clinical medicine, ethics and sociomedical issues. I found it particualrly useful during 3rd year tutorials.
Of course, there are benefits to PBL - most of your studying is done on yourt own - so you obviously must be motivated and indepedent learner. You have more free time and can make your own schedule (as opposed to schools which schedules classes from 8 to 5). And in the end, how much basic science did I really need to know? It would have been beneficial on the USMLE Step 1 (where PBL students traditionally do worse but they do better on Step 2; as I did) but I'm not sure it will make a difference during residency. I feel bad and insecure about it though, as my knowledge base isn't as deep as it should be.
Bear in mind that the above is MY experience and it was based upon a new PBL curriculum with lots of bugs: we didn't get useful lecture notes (if we got them at all), didn't have useful lectures BEFORE we had covered a topic and although the resources were there for learning the materials sometimes I found I learned best when I heard someone lecture about a topic.