Pros:

• Clear direction (orders, goals, etc.)
• Gets you in good shape (Training camps, etc)
• Nearly-full ride (College is still provided to people who enlist, I think. Plus, I believe there are benefits once you're out and even when you're still in)
• Possibility of travel (You'll probably be stationed somewhere for a bit, like Germany or some other foreign country. Japan, even.)

Cons:

• You have to respect authority (True for normal life, but doubly true for the military, as well.)
• Pretty much locked in for life
• Possibility of being hurt, killed
• Very strong and slightly-messed-up hazing rituals in most units, expect to be downright sexually molested for laughs
• Lack of privacy

There are some more, but that's the important stuff. Think hard about this. I'd suggest going to high-school and talking to a recruiter about a program they offer, that I can't remember the name of, where you essentially train to be an officer whilst getting a degree, paid for by the military, at your college of choice.