Upgrading to 3.0 is a nice milestone, especially if you're porting over a large app. ActiveRecord 3.x still supports the query interface used in 2.3, I'm guess

Upgrading to 3.0 is a nice milestone, especially if you're porting over a large app. ActiveRecord 3.x still supports the query interface used in 2.3, I'm guessing this is how they're able to run both versions from the same codebase. I'm not sure which Ruby version GitHub is on, but Rails 4 requires Ruby 1.9+. Running Rails 2.3 on Ruby 1.9+ is doable but tricky.