Jay Carney is a good press secretary for president Obama because Carney is very good at ignoring tough questions or blatantly lying to the press. In that respect, he is very good for his boss because he prevents Obama from actually having to own up to or be responsible for any mistakes.
His job is to knowingly spout BS out of his mouth that his superiors want portrayed to people whose job is to make him look like an A-hole. Every white house press secretary I can ever remember looked stupid doing their job, because it's impossible not to. It just comes with the territory.
When I watch his press conferences online, I struggle with the awkward method in which he answers questions. I know that he probably is getting lots of help in prep and even during the meeting but they could at least find someone a little smoother than him. Just my thoughts.