servlet 3.0 vs node.js for comet notifcations

I am developing a web app that pushes real time notifications to users comet style. My current solution uses Servlet 3.0. The general idea is that

1. a request's AsyncContext are put into a application scope Map,
2. a single background thread waits for notifactions on a queue
3. if a notification, it is pushed to the appropriate AsyncContext in the Map.

I am using Tomcat 7.0 with the NIO connector. In general, I am using a method very similar to this : http://www.javaworld.com/javaworld/jw-02-2009/jw-02-servlet3.html?page=3

I have not yet had the opportunity to explore node.js. Most of my use cases (likely) may not benefit from node.js, but perhaps this comet notification would.

As I understand it, both solutions would not have one thread to request, thus both system should scale.

My question is, what are the general pros and cons of using Servlet 3.0 Async mode or Node.js for scaling comet?