Just a quick note from an unbiased observer who loves MediaWiki and open-source...
Proprietary or not, Atlassian Jira is the best bug-tracker I have ever used, out of about 10 systems.
- Very configurable - You can create very simple bug forms for nontechnical users - Plug-in architecture for developing your own features & modifying app behavior (see https://plugins.atlassian.com/) - Helpful reporting capabilities that are easy to use - Its database schema is pretty understandable so you can extract data directly - The web interface doesn't do any stupid tricks that break in different browsers
If you're considering another bug-tracker, Jira is worth a look. (I have no affiliation with the product or the vendor, except as an end-user.)
DanB