They work in user-space and are portable, so I don't see the problem. Also, even if one opposes the idea of co-routines due to the problem of not knowing which

They work in user-space and are portable, so I don't see the problem. Also, even if one opposes the idea of co-routines due to the problem of not knowing which function will yield, there's no denying that they provide one of the best current solutions to the flow control issues with a clean upgrade path to generators when those become available in V8 in 18 months or so.