If you're on a modern version of upstart / Ubuntu - please don't use this upstart script. It will cause a variety of problems because of PID tracking issues.
What happens when you run it this way, is that upstart will run su, which will then run bash, which will then run Java. This obviously causes problems when you're trying to use upstart to stop your service, or monitor your service. Additionally, this can cause problems when bash dies (because, say an OOM), but the JVM is okay -- this scenario -- which has happened here at Yammer before, can cause problems.