It would be very cool if you entered in an issue, and Jira matched against existing issues.

If the match probability is good, then you could suggest:

"Are these issues the same? Would you like to add your report as a comment to this issue?"

"Are these issues related? Would you like to link them?"

In all cases, you could prompt the user to vote/watch the matched issues.

This would reduce the number of duplicate issues - and would enhance the quality of the information entered.