I applied to the HPSP scholarship (Navy, AF) and I was prior commissioned as an officer in the AF. I have been offered a Navy scholarship and the AF is supposed to let me know next week after the board meets. Here's the scoop. You owe one year for each year you receive the scholarship (they don't have 3 year scholarships anymore, only 4 year). This starts after your residency training.
The AF has a nice web site which might answer some of your questions. (http://ci.afit.af.mil/CIM/CIMJ/cimj.asp)
I think about 93% of this year's grads received their first choice of GME. Not bad. After your years of required service are complete, you will be put in the inactive reserves. You do not do a weekend a month, this is inactive. You don't wear a uniform (and don't get paid) and pretty much are a civilian except if a conflict breaks out, they can call you back to AD quicker if you are still on inactive reserves. You can request the regular reserves though and can continue to serve on weekends if you choose. Also, anyone can fly space A (Navy, Army, Coast Guard, retirees, cadets, etc). Not just AF people. It isn't as fun as it sounds. Sure, it is a free trip, but you are not guaranteed anything. I have sat in space A terminals for days and finally had to pay for a ticket to fly commercial because I couldn't catch a hop back home. You win some you lose some, and believe me, when you buy a commercial ticket on the spot and not 30 days in advance, you pay too much. When flying space A, allow lots of extra time.
Annual 45 days of ADT are paid at O-1 rate. Otherwise, you get ~465 dollars deposited in your account the 1st and 15th of each month for the remaining 10.5 months.
Commissioned Officer Training is held the summer prior to matriculating or after the first year of med school. It is about 6 weeks long and teaches you the basics (uniform wear, customs and courtesies, etc.) of being an officer. You are a 2nd Lt. for 1.5 months a year and never get promoted to 1st Lt. You skip straight to Cpt after graduation.
Also, they don't buy you an OMT table unless you are required by the school to have one (they pay up to $450 for it). They don't buy microscopes, they just rent them from the school. They don't buy computers, they can rent you one (But not rent to own). They only buy required books, not recommended. They pay health insurance if required, they also pay for the USMLE exam step 1 and 2, but not 3. They pay a certain amount for required items. If a stethoscope is required, they pay up to $125 for example. If you want the new digital Littmann for $350, you have to come up with the difference.
All in all, I think it is an extremely great deal. I loved my time in the AF and hope to get back in as a physician. Post if you have any specific questions. I would think you would all be more interested in life after med school once on AD. Talk to a recruiter, but take what they say with a grain of salt. They want to get as many people in and they have been known to stretch things and not tell the whole story. Not all of them, but some. Proceed with caution and talk to as many students or former recipients of the scholarship as you can.
BEST OF LUCK!!