Please read for an updated status on RailsCasts:
Learn more or hide this
GitHub User: rubinsh
I totally agree with you.
I think there should be another railscast to emphasize the real advantages of coffeescript :-)
IMHO a lot of the code that is written in the server side could have been written in the client side, but js can get so ugly and disorganized, that developers (my self included) prefer to write the logic in the server side.
with coffeescript - I believe things can and will be different.
not saying that business logic should be on the client side, but moving more code and calculations to the client side can make your application much more responsive and scalable.