WackoWiki has been using a Mantis Bug Tracker for quite some time now. We use this to track both bugs and the progress towards implementing new features.
Submitting a bug
To submit a new bug report or comment on a bug already in the system you must signup for a free account. Once the account has been created you can then select the Report Issue option which will then allow you to fill in all the information about the bug. The more information you provide the easier it will be for us to fix.
Browsing the bug tracker
You don't need to register if you just want to browse the bug tracker. If you want to see if a bug has already been submitted then head over to the View Issues Page and perform a search.