37signals has announced two upcoming products: Campfire and Sunrise. This is significant for Rails development because all 37signals applications has historically been the main source for new features in Rails.
Sunrise has already spawned a good number of features for 1.1. There are the polymorphic associations and join model support as well as form_for/fields_for. See the Pursuit of Beauty presentation for code examples on those. Campfire is pushing the envelope on RJS (more on that later).
Ill try to make the connection between new features in Rails and their origin in 37signals applications to make their usage more clear. Stay tuned. [Riding Rails]