At KDE we use Bugzilla with automatic status emails to various mailing lists and projects.

So even if bugs.kde.org were to go down, we'd still be able to fix code at git.kde.org, and use the lists.kde.org mailing list archives to lookup bug details as a backup. We'd probably use a mailing list system that doesn't suck like kde.markmail.org or GMANE for that last part, but that's just shaving the yak...

Fossil includes distributed issue tracking: http://www.fossil-scm.org

http://bugseverywhere.org/ does distributed bug tracking.

I've often wondered if we could store issues in a separate branch.

Also http://www.onveracity.com/ offers distributed version control, and distributed tickets, and wiki.