One thing that keeps me from considering Eventmachine mature is that the built in http clients are very crude and undocumented. Example: to get working error handling one needs to use an external http client library like igrigoriks em-http-request instead of the defaults. In this regard Node comes out ahead with better core utilities to boot. Stuff like that is very confusing for new users and puts the whole framework into question (shipping with a http client that is not suitable for production use).