I made the transfer from AFROTC over to the Marine Corps. I was one semester away from commissioning into the AF and had an alcohol related incident that resulted in me being disenrolled last January. I had been in ROTC for 3 1/2 years, pilot slot, outstanding cadet, but still recieved a 3 on DD 785 (needs of service). I went to the OSO and told him my situation and he told me that he would give me a chance. That's all I needed. I got a recommendation letter from my PAS and worked like hell to show my OSO that I was serious about being in the Marines. Took the air test, got a waiver (credit due to my OSO), and started some hard core PT. I couldn't even do 1 pullup at the time. I went to OCS last summer and am now a 2Lt waiting for TBS. All this in less than a year. It can be done, but make no mistake that it is a different mentality and much more intense. If you're looking for an air slot, it may be easier to do the PLC program than the OCC...I had to extend for a semester of school to do PLC. Right now I do believe they are still letting cadets get out (a buddy of mine just got out last semester). Looking back, I definitely think the Marine Corps is a better fit for me......blessing in disguise. Hope this helps.
P.S. You will find that most OSOs will go to bat for you if you show them that you are dedicated, no matter how long they've known you.