Pros
I loved being able to live outside the U.S. for a while and I got to experience living in Japan. I've always wanted to go there and it was a dream to be able to live there. The Navy provides you free health care, dental, some life insurance and career training in whatever job you're in. Also use the Post 9/11 GI Bill!!! It's the best reason to join. It was a the first and so far only job where strangers looked up to me for doing it and that never got old.
Cons
Choose your rate, choose your fate. You hear that a lot in the Navy/Military. If you're going to join, go in with your dream job in mind and do not let them talk you into another. It may take you a bit longer to get it but it's very much worth it. The Navy can be a very tough job and if you like what you do it will help you in so many ways. Also don't listen to anyone about how great career opportunities are after the military. Just cause you were in the military doesn't mean employers are going to choose you over the next guy. Whatever you do in the military try to make yourself more marketable for the outside world because everyone gets out sooner or later.