Here is what I cut from a letter I sent to someone else regarding similar questions, hope it helps.:
"I like it so far, especially since all
this crap happened last Tuesday, all the sudden it seems like I have picked
a great career path. I've been in the program now for close to 4 semesters.
Basically, it is a lot of application paperwork, testing, and basically the
Marine Corps. just making sure that you are a good candidate for the job.
After you are in the program, the only things you are required to do is call
the OSO office once a week and check in. Let them know that you are still
in school, aren't in jail, and doing okay. Supposedly, if you want to opt
out of the program you can at any time PRIOR to the day you are commissioned
(ie grad day).
There are two ways to get money from the Marine Corps while you are in
school Financial Assistance Program (FAP) and College Tuition Assistance
Program (CTAP). FAP is nice, it gives you $900/semester the entire time you
are in school but tacks on 6 months to your term of enlistment. A sidenote
to this: if you drop the program or the program drops you, you DO NOT have
to pay this money back. CTAP pays for tuition and books (up to $6000), adds
1 year, I think, to your contract, and you DO have to pay it back if you
leave the program for any reason. I am taking advantage of FAP, but not
CTAP, just in case I change my mind or want out of the program for some
reason, I don't wanna haveta give the Marine Corps thousands of dollars to
get out.
As far as OCS goes, it is a different experience for everyone. Some
guys told jokes and had a good time, others cried and dropped out. It
depends on your outlook on life and how much you have suffered prior to
going there. You will hear some people say that Parris and San Diego are
more difficult, but we had guys who made it through that drop out. The
reason OCS is tougher is that the level of physical fitness expected of an
Officer Candidate is higher than that expected of enlisted recruits. At
basic they start out at a very low level, and progress to a high level, this
way the most unfit people are fit by the end. At Quantico (officer
training) they start us out at a high level and maintain that through the 4
'real' weeks of training. Don't let this scare you, if you are moderately
fit, you will do fine if you try. My three-mile run time was just under 20
minutes when I got there, it stayed constant. I did 16 pull ups the day
before I left, and did 8 the day I graduated (your body breaks down BAD
while you are there). Crunches stay the same. Everyone you know will give
you lots of advice about training, listen to all of it, and whatever they
say they did, it is only half as bad as it sounds

Oh, and I went to OCS
juniors 2 summers ago. They supposedly made it easier this summer to get
recruitment numbers up and scare less people off. When I went 270 people
graduated junior, while only about 100 people graduated seniors, a lot of
people go, graduate, and then don't go back. If I could do it again, I
would probably go to the single 10-week session. If you have any more
specific questions about OCS lemme know and I'll tell you what I can.
I'm trying to think of other good info to give you...basically if you
want to fly it seems like a good way to go, I'm a little worried about
getting assigned to choppers, I would much prefer fixed-wing, but hopefully
it will all work out. I just got called today to go and get my flight
physical on friday, so I'll go and do that if all goes well and I don't have
some horrible disease I don't know about, I'll be going back to OCS this
summer for seniors. Anyway man, good luck with your decision, do what makes
you happy, get EVERYTHING from your OSO in writing, and read all the fine
print. Oh and they are prob gonna try and get you to sign up for PLC and
then later actually get you assigned to PLC-Aviation, that is bullshit,
don't sign until you pass the air test and make sure you get what you want.
You will spend a huge chunk of your adult life in the Marine Corps once you
sign, so if you want to be a pilot, don't settle for less, there is always
COMAIR Academy, FlightSafety, etc..."