Rails 3’s been a work-in-progress for around about two years now - and as of last night it’s ready!
For a descriptive list of changes, check out David’s blog post here: http://weblog.rubyonrails.org/2010/8/29/rails-3-0-it-s-done
The Rails tutorial has also been updated (for the most part) - and is available at http://railstutorial.org/chapters/beginning
To install, just use the gem package manager to install the latest rails gem:
gem install rails --version 3.0.0