Not sure it's fair to say Rails is stagnating. Rails 3 (particularly with the improvements in ActiveRecord) is significantly leaner and nicer to use than Rails 2.
New API for ActiveRecord, modularity, merging with Merb are very important, but it's not a game-changer. Rubinius and RubyMine on the other side are game-changers.
I wouldn't say Rails is stagnating, I'd say it is maturing.