I met a Cumberland Presbyterian during fall semester and we became fairly good friends. The main difference, as he told me, is that they reject Calvinism, or the Doctrines of Grace, or whatever you call them.
Which is a fairly irritating thing you might imagine! I asked him why, and as is typical with most free-willers, the responses were based on erroneous ideas of God and human-centered logic (which isn't very logical).
He said that he didn't believe in analyzing the Bible, but rather just read two chapters a day and let it at that.
Whatev, he's a nice guy and we get along fine. I just really disagree with stuff like that.