I'm currently a 1st year at SOMA, so I can't speak personally to the way the curriculum prepares one for the board (yet). But ironically, we had a panel of upperclassmen speak to us just the other day and this topic came up.
Obviously everyone studies independently or though a prep-course for the boards. That goes for every student at every medical school in the country. SOMA is no different. But what the panel did say was that everyone seemed to do just fine on the boards, that the people who struggled passing were the people that were struggling passing school at all. And that your performance in class seemed to fairly accurately predict your general performance on the boards. People in the top 10% of the class pretty much scored at/near/above the 90th percentile on COMLEX etc.
All our professors are required to register to contribute questions for the board examinations, part of the gig of teaching at SOMA (not sure if this is a universal requirement at all schools). And students have singled out some of our professors as having exam questions that were exactly like those on the boards.
We have talented faculty; our Path professor is the Maricopa County (Phoenix metro area) medical examiner; our main pediatrician is very well respected in his field; pharmacology professor is also with Mayo (I think). Our clinical faculty are all extremely good. No complaints really.
The scheme based curriculum really doesn't give you any excuses for not scoring well on clinical questions either. I'm very pleased overall with my education so far.
Finally, the 1+3 curriculum only increases my confidence for boards. I'm learning the bulk of the basic and clinical sciences this year, then next year I'll spend the year putting them into practice. How could that be bad for prep?
Hope that helps, and if this thread is still going next summer, I'll have a lot more to say I'm certain.