I'm confused. Rails 3.0.8 is the current version. Rails 3.1 is still in beta. What's in the beta release of Rails 3.1 that caused you to leave? A couple of defaults have changed, but valid Rails 3.0 applications can be upgraded to 3.1 with a minimum of effort.
When I tried the Rails 3.1 beta, I had issues with getting Mongoid and various other dependencies working and could not get it to run. My Rails 3.0 app completely broke. I might be an edge case though.
I'm preparing a screencast on upgrading the Rails Tutorial sample application from Rails 3.0 to Rails 3.1. Maybe you'll find it useful. Subscribe to the news feed (http://news.railstutorial.org/) to be notified when it's ready.
Have the gems for Mongoid and such been "certified" against 3.1? Seems kind of hash to drop the whole framework based on a bad beta experience...wait until an official release and see.