I really don't see what is so difficult here guys.
The bottom line is this...did George Zimmerman feel his life or the life of another was in immediate danger of serious bodily harm or death? If yes, then he has the right to stop the immediate threat (I can see after looking at his injuries why he might think he was in big danger). If no, then he does not have this right.
So, did he or did he not think he was going to be seriously injured or perhaps even die? That will be for a jury to decide but once that jury sees those injuries on his head, two black eyes and a broken nose, I don't see any possible way to convict him.
You could say the exact same thing for Trayvon except for the injuries part, because he took self defense in to his own hands and whooped some ass old school style.