<p>First, let me correct myself: first semester at MIT is P/NR, second semester is ABC/NR. Official website rational states:
[quote]
P/NR and ABC/NR are designed to reduce the anxiety and pressure that freshmen often feel in their first year. P/NR and ABC/NR also provide an opportunity to learn how to balance academics with extracurricular activities.</p>
<p>MIT students come from very diverse school systems that provide different levels of preparation. P/NR focuses on the process of learning rather than the outcome, and ABC/NR eases you into being on grades, as you will be as an upperclassman.
[/quote]
There is a thread on the MIT board here discussing medical school admissions and the effect (if any) of the MIT first semester P/NR policy. The short answer seems to be that few med schools demand that MIT release the actual grades for first semester freshman, Johns Hopkins being the one people mention most often.</p>