Before the most recent revision of the firefox addons site, Vanilla 1 was used as the discussion tool for addons for Firefox.
Despite this fact, Vanilla 1 didn't scale well. Vanilla 2, on the other hand, handles load much better. We're working on making core changes so it can handle extremely large sites. We're also working with some partners on doing big implementations. We'll be showing these on the homepages after they're up