With a pair of coroutines working togetger, you are unlikely to get synchronisation problems unless they are badly written. However, in the more general case of continuations, I don't think you can disregard synchronisation problems with coroutines, in the same way that you can't disregard sync problems with emulating threads on a single CPU.

If all your locking or resource acquisition is done in a single step, then you should be ok, but if there are any yields in between resource acquisitions, then you need to avoid deadlock. I suppose the co-operative nature of continuations means that you can avoid them easily, so you may be right.