Another thing to consider is joining the IHS (Indian Health Service) AFTER you graduate. I, too, have considered NHSC (as I am at one of those unfortunately "super-expensive" schools), but the contract is very limiting and doesn't give you very much flexibility (as other posters have noted).
You can join IHS after residency, and they pay about $20K per year towards your loans, plus paying you for working as a physician. If you want to go back to Alaska (as I do), there are plenty of options, including those listed in other posts (including the Alaska Native Hospital in Anchorage).
This way, if you're not sure what you want to do (as most 1st and 2nd year students don't), you still have options without entering into a strict obligation. if you still want to do primary care, you can get your loans repaid. And if you end up an orthopedic surgeon, you won't have to worry about either service commitments or loans.
If you aren't REALLY sure of what you want to do, don't do NHSC--I, for one, have changed my mind about my specialty about 15 times in the past 2 years.
A funny aside--last year, when talking to the financial aid advisor here in NYC about NHSC, she really tried to discourage me from applying. "You never know where you'll end up," she said. "You could even be sent to some god-forsaken place in ALASKA!" I had to laugh, and then reminded her that I was born and raised Alaskan, right down to my "Alaska Grown" Palmer State Fair sweatshirt!