I applied through a recruiter. The process took 3 days. I interviewed at US Marine Corps (Seattle, WA) in Nov 2011
Interview
Talk to recruiter and ask necessary questions to make sure the Marine Corps will be right for you. ALWAYS ASK FOR A SIGNING BONUS! Be physically fit and ready to go to boot camp before you go to boot camp. It will make life easier.
I applied in-person. I interviewed at US Marine Corps (Washington, DC)
Interview
It was a very easy but a lot of paperwork. Interview consisted of medical check, mental health check, and a drug test. There were multiple tests that had to be taken on a computer and a very long background check.
This was a tough interview process and the screening was rigorous. It will take a long time. I recommend getting started early. This is a long term commitment. You need to be ready for it.
I have to do this for some reason to get access to the GD's website. Interview process, walked into the recruiting office and said "sign me up". Recruiter was a friendly guy, said "Ok!".