I think it's a pretty cool name. I have an ancestor named Cormac MacCarthy and that was the first time I heard the name. I doubt I would use it though because I live in the USA where the name is not used (or at least not often).
I prefer the charioteer and raven meanings. I can't imagine the name would become so popular in early Ireland if the prevelant meaning was son of defilement. I could be wrong, though. There could have been a lot of defilement going on.
Cormac is an interesting name. And one could go by the nickname "Cory" or "Mack." Sadly, the meaning is not too pleasant. The meaning is: "son of defilement." Defilement means to make impure or unclean; to violate or deflower. So, in a sense, the meaning of the name could be "son of rape" because rape is of course an act of impure violation.
I love this name. Its sounding, very masculine and chic. Who cares about the meaning? No one goes around introducing himself like "hello, my name is Cormac which means "son of defilement"".
I love this name, it's the name of my fiance's nephew and he is too cute at almost 5 months! Unfortunately I can no longer use it my son's name. Also the character in Harry Potter is named Cormac McLaggen.