The state of distributed bug trackers
A whopping 5 years ago, LWN ran a story about distributed bug trackers. This was during the early waves of distributed version control adoption, and so everybody was looking for other things that could benefit from decentralization.
TL;DR: Not much has changed since.
The potential benefits of a distributed bug tracker are similar to those of a distributed version control system: ability to fork any arbitrary project, easier collaboration between related projects and offline access to full project data.
The article discussed a number of systems, including Bugs Everywhere, ScmBug, DisTract, DITrack, ticgit and ditz. The conclusion of our favorite grumpy editor at the time was that all of the available distributed bug trackers were still in their infancy.
All of these piggyback on a version control system somehow - either by reusing the VCS database, by storing their data along with the source code in the tree, or by adding custom hooks that communicate with a central server.
Only ScmBug had been somewhat widely deployed at the time, but its homepage gives me a blank page now. Of the trackers reviewed by LWN, Bugs Everywhere is the only one that is still around and somewhat active today.
In the years since the article, a handful of new trackers have come along. Two new version control systems - Veracity and Fossil - come with the kitchen sink included and so feature a built-in bug tracker and wiki.
There is an extension for Mercurial called Artemis that stores issues in an .issues directory that is colocated with the Mercurial repository.
The other new tracker that I could find (though it has also not changed since 2009) is SD. It uses its own distributed database technology for storing bug data - called Prophet, and doesn't rely on a VCS. One of the nice features is that it supports importing bugs from foreign trackers.
Some of these provide the benefits you would expect of a distributed bug tracker. Unfortunately, all those I've looked at fail to even provide the basic functionality I would want in a bug tracker. Moreso than with a version control system, regular users interact with a bug tracker. They report bugs, provide comments and feedback on fixes. All of the systems I tried make these actions a lot harder than with your average bugzilla or mantis instance - they provide a limited web UI or no web interface at all.