I have trackbacks turned on (I was hopping to use it with confluence but no luck there), We posted an issue on our jira which does not have anonymous access, that had a link to another site that happens to use trackbacks. Even though we dont allow anonymous access a portion of the issue report showed up on their site:

http://stlq.info/archives/002009.html

Scroll down and you will see [KWS-933] and above that some of the text from the issue.