We could do lots more in the Ant script to ease webapp installation:

• Get the user to select a db type from a drop-down list, and have a
  @token@ in entityengine.xml that is replaced.
• Download extra required jars for the user's server, with <get>
• Prompt the user for database connection details, and:
• auto-generate Tomcat/Resin/Jetty XML descriptors.
• use collected db config details to ensure JDBC connection works.
• create a clean database, and maybe a 'jira' user, using <sql>.

• Install JIRA as a Windows service.
• Fetch and run another Ant script from www.atlassian.com, which in turn
  downloads and applies hotfixes.
• ...