i just received the scholarship last week but after doing a lot of research, including a lot right here on sdn, i turned it down. there are tons of other threads here on sdn about military scholarships. there is a lot of good, bad, and conflicting information regarding hpsp. some people love it while others loath it, and a fair amount are up in the air (which was reason enough for me to be pretty sure i didn't want to risk it-- everyone pays off their loans eventually without a huge problem anyway).
i would check out the other threads-- there are a bunch under allopathic, and few under both allo and osteo premeds.
a lot of the other threads have links to websites that are also helpful.
if you have any specific questions, you can pm me, and i'll give you my opinion, but since i haven't accepted the scholarship, my thoughts and opinions are based only on the research i did, the people i spoke to and my completely misinformed recruiter . i don't want to be a hater or anything, but my overall conclusion is that the scholarship makes life during med school a little easier, but you'd better really love the military afterward if you know what i mean. good luck!