I recently used embedded Jetty for a small REST server project and it was a revelation. It took exactly no time to get it running and now I can deploy web-apps just by starting a runnable jar. That’s reason enough – no more Tomcat with all the complexity of sharing a single server amongst multiple apps, but, even more importantly, its wonderful for development. No more fooling around with Tomcat in Eclipse – just debug web-apps directly as a Java application.
We run all of our apps as multiple instances behind a load-balancer (HAProxy), so its convenient to run each app on a separate port and let the load-balancer handle the forwarding from port 80.