I have tried to approach CoffeeScript a couple of times, but every time using it for real has had lots of doubts:
- New syntax to learn, both myself and other team members
- New tooling needed
- Debugging story not that good (although getting better)
- Will it fly? Do I need to roll back to JS in a year or two?
Overall I have not felt that the benefits would outnumber the drawbacks.
I do not see myself writing any apps in TypeScript, at least not in a while, but I will follow the project very closely and play with it every now and then. You never know, it might even fly – especially if the community gets over the fact that TypeScript is Microsoft-initiated.