One thing I want to add: apparently, if you are an officer are eventually retire, that's not the same as officially resigning your commission. If you don't resign your commission, the service can call you back any time until age 60. And right now, they're not letting retired officers resign their commissions. There is the potential that as an officer, especially with things as they are now, you'd be taking on a lifetime commitment that you don't expect.
Follow this URL:
http://www.sftt.org/dwarchive.html
Once there, click on the link for the 9/21/04 article, "Is a Commission a Life Sentence?" Can't send you directly there, because the articles are Javascript popups.