I almost went the HST route, but ended up choosing a different school.
NP struck me as a little too lax... I didn't have much faith in a program with such a loose structure. The society system is very cool though; this should be adopted by other schools. I know that NP students end up as very competent physicians, but I'd be a couch potato without structure.
I was attracted to HST by the emphasis on research, but ultimately I wasn't quite ready to seal my fate in academia. I was a little bummed to see it overrun by MD/PhDs... I was hoping that HST would be geared more toward research-minded MD folks. HST students have fantastic resources at their fingertips, and if you're certain that you want to balance your time between the lab and the wards for the rest of your life, then HST is for you.
In the end, I chose Hopkins, since it had the research opportunities (albeit less structured than HST) without the implicit obligation to remain in academic medicine.
Cheers,
doepug
MS III, Johns Hopkins