Tell you what, we mix it up a bit at Tulane ...
We do about 90% traditional and about 10% PBL.
What I like about traditional:
They tell you exactly what you will eventually need to know for the test. Then they teach it to you. Then they test you on exactly what they said they would test you on.
What I don't like:
I hate waking up early. So, I don't. Which means I learn all this stuff on my own anyway. Which makes medical school a really expensive self study experience. But, I do learn it, somewhat.
What I like about PBL:
It's real cases. Usually, a Tulane doctor has an interesting case, and they write up the case with a prof. Or, they just make up a case, just to review all the principals. The cool thing is, if you have studied, all the stuff comes together and you see how the stuff you learn will work in a clinical context. And that is money. And, near exams, it's a great way to put together some of the major concepts (acid/base was cleared up for me in a PBL). Best of all, they are always in the afternoon, which means I have no problem coming.
What I don't like:
It's too proctor/group dependent. Sometimes both suck. Also, if you aren't prepared, it friggin blows, b/c it just reminds you how far behind you are. These two problems are HUUUGE, and that's an important reason why I'm glad we aren't too PBL dependent.
I think we should have slightly less lectures and slightly more PBL. Like one a week for the entire year. Or maybe 3 every two weeks. So, that would be about 35-40 cases. We've done about 15, I think.
But, I think based on what USMLE looks like (I'm a first year, so I don't much about it), I think it would be foolish to think a PBL curriculum would prepare you for Step 1. PBL alone won't do it, you have to put in a lot of your own time to do really well. B/c there is only so much you can learn in a PBL ... the PBLs don't focus on weird ass things like Lesch-Nyman or Hurler's, they focus on important things like diabetes management or an MI.
However, the cool thing about a full PBL curriculum is that you would have so much free time to study for the boards, while preparing for the cases. So, it could work if you were decently disciplined.
Good luck,
Simul