You've already received the posts that talk about the military commitment. One caveat - the 7 years does NOT have to be AFTER residency. You could choose to serve for 7 years as a General Medical Officer, Undersea (Diving) Medical Officer, or Flight Surgeon (this applies to Navy only BTW) and get out without having completed a residency. So, to clarify, you have a 7 year obligation, and the time spent in residency training does not count towards that obligation.
Now...as far as the quality of school goes, I have never met an individual that graduated from the school that regretted attending it. I know of several people (my wife included) who turned down acceptances at some very prestigious schools to attend USUHS. It all depends on what your goals are. If you are interested in attending the school only to avoid debt and make some money...I think you will ultimately be unhappy with your decision.
I highly encourage you to do your research before you proceed with the application process at USUHS.
If you have any other specific questions, please do not hesitate to PM me.
Cheers.