Currently, the output of the script task is not useful for debugging, as it does not show the commands that are executed. Instead, the logs show something like:

/bin/sh /opt/app/atlassian/bamboo/current/temp/DEV-JOB1-8-ScriptBuildTask-6385738016401102851.sh

Rather than:
05:59:05 [atlas-web-promote] $ /bin/sh -xe /tmp/hudson1289015703492215660.sh
05:59:05 + ./my_script foo bar

Where a script is called using arguments generated dynamically, or pulled from Bamboo variables, this is essential. Perhaps an option on the plugin that gives the equivalent of running under sh/ksh/bash -x?