Yes, there is a limited number of contracts with the USMC.  I received the flight contract a year go.  I went to OCS, and will be graduate in the May '08.  Then to TBS  I GO, after that the funs starts at flight training.  Yes the contracts are true.  I've talked to a lot of marine pilots and others.  If you receive a flight contract you WILL  have a chance to go to Naval Flight School to become a Naval Aviator (pilot).  Even if you are at TBS and are a below average marine you will still have the flight contract and will still be heading to flight training once you graduate TBS. 

OK now i will tell you about the competition.  This whole process is very very competitive and demanding.  I heard my OSO tell me that for every 1000 individaul that is calls him.  He will commission one.  This isn't the Navy, or Air Force.  This is the Marine Corps.  The Few.  The BEST!  Getting contracted is hard and even harder to get air.  The air contracts are limited and just cut it about 2/3 number of air contracts last year. Only a few applicants will get a air contract form each OSO.  At OCS about 1-2 candidates out of 10 will have a air contract.  Being a air contract a OCS you are given a harder time.  Because the instuctor know that you wont to fly and for some stupid reason they will hate you for it.  OCS is VERY DEMANDING and very hard.  For ten weeks you will be in hell.  This will be hardest physically, mentally, and emotionally thing you've done it's designed to make you quit.  About 30% of the candidates will not graduate.  You are trying to prove that you can lead marines in battle.  The only way to test you and see if you can lead with the stresses of battle is to stress you completely out and see how you react to it.  So, all OCS does is ten weeks of pissing candidate off and seeing how they react to it.  Once again this is the marines.  I know a couple of guys who wents to ARMY OCS and AIR FORCE OTS.  When i tell them what i went thought they are blown away.  Their OCS  was a joke compared to MARINE OCS.   The hardest ten weeks of my life was OCS, and i'm a track and field collegate athlete.  These marine instuctors are very good at getting into you head.  Once you let them you WILL break down and quit.  I've seen it happen and it's sad.  

If you wont to be garanteed to fly before you sign your life to them.  The Marine Corps is the only way to go, but it is the hardest way to go by far.  Marine aviators are regarded as the best and it takes the best to acheive that goal.