Ref: http://www.atlassian.com/software/jira/docs/latest/csv_import.html

We ought to import the CSV importer code into JIRA, and make it a separate page like the Bugzilla importer. We could then remove the need for users to discover the project id. The import JSP and example needs some general cleaning up.

The chief impediment to this seems to be finding a CSV library that handled Excel's format. We currently use ostermillerutils_1_02_21.jar which is GPL, so we can't redistribute it.