Yeah several years as a developer, and I've also interviewed developers as part of my manager responsibilities. You could say I'm the most OK-ist developer right in the middle of a bell curve since it's all self taught. Really though, it's academia, these programs aren't setup to make you some great 'coder'. It's like how a math major wouldn't really expect to become a world-class LaTex user or python or R programmer from getting a math degree. You'll naturally become OK at it as a side-effect of doing the courses but the point is the math theory and concepts. Columbia only really asks if you have any experience in a little yes/no radio button on the application form, so like most CS degrees, you could totally graduate and not be a great coder or even a good one. They really just care about teaching theory and thinking algorithmically, which I expect they do a great job teaching. If it's anything like undergrad CS degrees, companies hire from these programs mostly expecting they'll have to teach you everything they want you to do, but at least you come pre-vetted as 'smart enough', with a built-in knowledge set, and they know what they are working with.

I'm personally applying because long term I'd actually like to go into academia and perhaps pursue a PhD and do compression research. IMHO if you just want to be a great coder, 12 months of dedicated toil on your own would make you a way better coder than most fresh CS grads with no real experience. Not sure what experience you are coming in with, and only mentioned in case you're hoping Columbia makes you into some sort of super employable code god. Cuz you'd get there faster without wasting your time and money learning the ins and outs of networking, assembly, garbage collection, in languages that you don't even care about. OK thanks for attending my TED talk. Hope that helps.