@Jan, today many applications have a repository on GitHub just to track bugs and features requests via Issues, even closed-source commercial apps.
For example, Sublime Text relises on a GitHub repository for all bug reports and features request, instead of its official forum (in fact, if you report a bug on the forum you get asked to report it on GitHub instead):
This makes it easier for both developers and end users to create and track status of bugs and features requests, for although GitHub is not a dedicated tool it nevertheless offers quite powerful features with Issues, milestones, projects dashboards, etc. The advantage over the forum is that Issues have labels (ie. tags), which allows quick filtering, and can cross-reference each other as well as any GitHub repository, issue or pull-request.
As an added bonus, this repository would also get a version controlled Wiki, which anyone could edit via the web interface.
Begin GitHub popular as it his, chances are that a good number of users will already have a GitHub account, and any PM related project could easily cross reference with these issues.