I worked at US Marine Corps full-time (More than 8 years)
Pride, lifetime friends/family, discipline, travel, experiences that will last a lifetime, being a lifetime member of the world's finest finest fighting force...
"The Marine Corps, in theory, is a perfectly run organization. It's the people that screw it up."
I applied through a recruiter. The process took 8+ months. I interviewed at US Marine Corps (Kent, OH) in May 2011.
You will be taken to MEPs and take an ASVAB, which will help them determine what positions you are best fitted for. You can choose to go in under a specific contract, or choose to go in under an open contract. An open contract is where the Marine Corps will decide what MOS they need you for, and where they want to send you.