Yes, we have an internal tracker but it's not practical to open it up to the public in its current state.
My main issue with using a public tracker is that that they all seem to either be cumbersome or riddled with security holes. TRAC for example is a great product, but does about a million things we don't need and requires maintaining a separate Python environment for hosting. Bugzilla is ugly and cumbersome as hell to use and again, requires mod_perl and a bunch of other stuff that we don't normally run. There's no technical reason we couldn't install either, it's just a lot of work to maintain/audit a separate machine and/or application stack just for an issue tracker.
I've almost been considering just using a separate section of SMF as a public bug tracker. Might be a bit hokey, but we're already maintaining it so it requires no additional maintenance/administration overhead; each thread could represent a single issue, and SMF already supports polls where people could vote to prioritize issues.
Or if anyone else has any suggestions for a bug tracker that's reasonably lightweight and has a decent security track record, I'm all ears.