Old, yes, but relevant. I eventually went with an implementation of Pligg CMS. It's an open-source version of essentially what Digg does.
www.pligg.com
Someone even built a vBulletin bridge that sort of worked between Pligg beta 9.1 and vB 3.6. It doesn't work anymore and has been abandoned. My own implementation can be viewed here:
www.blackbus.org/ideas
At this point my Pligg is stuck at 9.1 and I can no longer approve new submissions. If I upgrade to the latest version of Pligg I can't use my custom template as their templating system changed completely somewhere along the way. And so it sits.
For a while it was awesome though.