Many agree on the fact that there are cases when it is best to go for Ruby on Rails instead of some java-based technology.

Are there any experiences concerning the questions, when it is more advisable to go for J2EE or Spring/Hybernate/Tapestry stuff instead? I would be most interested in some feedback from people who generally accept the usefulness of Ruby on Rails, because that really contributes more to the point. But answers in the flavor that J2EE is always the way to go are off course welcome as well...