What Makes a Programming Language Successful?

danielstoner writes "The article '13 reasons why Ruby, Python and the gang will push Java to die... of old age' makes an interesting analysis of the programming languages battling for a place in programmers' minds. What really makes a language popular? What really makes a language 'good'? What is success for a programming language? Can we say COBOL is a successful language? What about Ruby, Python, etc?"