We owe the people that made Rails 3 possible a big thanks for this. With the encoding issues sorted out, 1.9.2 has changed from a pain in the neck platform to a completely sane and viable platform. Which is probably the biggest reason why Heroku can make this move.
We've been using 1.9.2 for client projects since the release of Rails 3. It's been a great move with very few code compatibility issues. 1.9.2 provides a very solid boost in performance over 1.8.7, especially when rendering ERB templates, which makes a surprising impact on user experience for complex views. I've seen 3-4x decreases in ERB rendering times just switching between 1.8.7 and 1.9.2.
This isn't about scaling the web tier, which is fairly trivial, it's about being able to bring a request that took 500ms to answer down to 200ms. That can have a very real and appreciable impact on user experience.
How about a 1.9.2 compatible heroku gem ? Do I still have to run heroku commands on a 1.8.7 ruby ? Last time I checked it was still binary-tied to 1.8.7.
