DHH’s RailsConf 2010 Keynote Video: A Justification of Rails 3.0
DHH gives an insightful and accessible 38 minute walkthrough of some of Rails 3's differences from Rails 2.0 and explains the motivations behind them. A particular focus is given to improvements made to the routing system (both for REST and non-REST URLs).
I've been a bit lukewarm on Rails lately, opting instead to strongarm Sinatra into doing whatever I want, but DHH's keynote is a compelling overview that encourages me to give it a fair look.
The final release of Rails 3.0 is expected within the next few weeks, with a release candidate in the next week or so.