What vampsoul said.
However, I'm not TOO sure about the academics. From what some current cadets have told me, the teachers try VERY hard not to fail you. This is why West Point has some of the most accessible professors, so they said. Makes sense to me, as I'm sure the Army would not want to fail its future officers, since that will prevent them from getting into the Army. That's not a very good investment I would expect.
The cadets have also told me that before junior year there is a contract you need to sign before you continue schooling. When you sign this contract, it forces you to stay in West Point and serve in the Army soon afterwards. I'm sure this is when people decide whether or not the Army lifestyle is for them.
Medical stuff is kind of iffy for me. From what I'm hearing, breaking a bone will prevent you from staying in the school? Or at least, you'll have to wait a year. I'm not sure about this one, if anyone can clarify, please do.
Trouble with the law can also screw you up. I read recently of some USNA Midshipmen who were kicked out for having a marijuana-like substance. Just don't do drugs.
Please feel free to correct me or add on, this was just a compilation of inputs I received from current cadets as well as alumni, so there could be discrepancies.