I've just got a Bugzilla account for SWAD-Europe work, as part of W3C's Bugzilla installation. To find out more about the facilities it offers, I am experimenting with a 'component' for RubyRDF, my Ruby software tools. If I can fix enough of the bugs to make it useful, I'll probably use RubyRDF as a basis for a number of demos through the SWAD-Europe project.
Bugzilla is interesting because it is used on quite a few projects that work in public, and so various people are working on add-ons (RSS feeds, RDF views etc., email interfaces...). I'll know more about it once I've used it a bit more...