Pros
great benefits: especially with the new GI Bill, if you just graduated from high school and you are not ready for college or don't have the means to afford it, give your four years and uncle Sam will pay you to go to school. (that's right boys and girls, not just your tuition but also rent and bills) opportunity to travel the world: this really depends on luck but on a ship you will visit a few countries medical, dental, etc. camaraderie
Cons
Lots of Bureaucracy ("To change anything in the Na-a-vy is like punching a feather bed. You punch it withyour right and you punch it with your left until your are finally exhausted, and thenyou find the damn bed just as it was before you started punching." -FDR, that was 70 years ago, but it's still the same) You have to sign 4+ years of your life. There is almost no legal way out (such as winning the lottery,) so do not rush into it. Lots of menial tasks Just because you signed up to be a electrician doesn't mean that you will be repair electrical equipment all day. You will clean toilets and wash dishes, stand watch for 5 hours in the freezing cold or the blistering sun with all your gear, etc.