Developers Touting Ruby on Rails' Enhanced Performance
This release includes a faster version of Active Record, which is the basis for models in Rails apps, data validation and database independence.
Speaking about the performance boost, David Heinemeier Hansson, founder of Rails, stated in a blog post "How about some free speed? Well, here you go. Rails 3.0.3 includes a much faster version of Active Record that reclaims the performance lost when we went from Rails 2.3.x to 3.x and then some."