Sorry... didn't notice this thread before today.
Lots of people take time off for various pursuits. It typically happens after third year though, since most people are anxious to get some long-awaited clerkship experiences before taking a break.
For my class (2004), in the last year...
~20 (no kidding) are taking a year for an MPH
2 people entered law school
1 person entered grad school for music composition
1 person entered an MPP program
A few non-MD/PhD people are doing a research year
There are probably others who are slipping my mind at the moment, but the bottom line is that there are plenty of opportunities for Hopkins students to explore medical and non-medical interests.
Hope this helps,
doepug (MS IV, Hopkins)