We use JIRA to track all our issues (bugs, new features, suggestions, etc.). Anybody (who goes through the trouble of creating a JIRA account) can add a new issue. Before you do so, please check if the issue already exists by using the search functionality of JIRA. When in doubt, don't hesitate to ask on our mailing list.
If you've found a bug, we would love to also get a test case that reproduces it. Even better, if you know how to fix it, please consider donating the fix by adding it as a patch to the issue.