Yeah RJS was a clusterfuck, but hindsight is always 20/20. At the time it was a new idea that was being explored that just didn't pan out. The Prototype dependency dates back to 2004 when no framework had AJAX support, and the code just started getting stale from there and didn't get any attention until Rails 3.

Anyway, I agree that Rails core has traditionally been far from the savviest of JavaScript developers, but the nice thing about Rails 3 is that they've finally achieved reasonable modularity with all the components, so there's not much pain in getting around Rails opinions anymore.

As for CoffeeScript, I'm still on the fence, but it's clear that Jeremy Ashkenas knows his JavaScript, and his work is not done out of ignorance, so I'm glad for it to get more exposure.