Digg is also similar to Firefox’s StumbleUpon or Stumble for short. The more people who rate positively, the more other people see the site. I find all these Digg links on FR annoying myself. It’s only started happening in the past few days that I can see.
The Digg threads are new - and you are right, they are certainly growing. Maybe as the popularity continues it would be worthwhile to add a “Digg” forum to sort of corral them.