I read an interesting article a few weeks ago comparing Ruby on Rails to the popular J2EE stack of Hibernate/Spring/JSTL. This is not really a meaningful comparison, but Ruby on Rails is a very interesting technology. It waves the mythical carrot of zero (or close to zero) configuration in front of the faces of developers and managers. It is one of the most aggressive attacks on that problem that I've ever seen.
Of course one of the most surprising things about RoR vs. J2EE is that no J2EE vendor has ever come up with something like RoR and sold it. The most obvious vendor for something like this is Oracle. They have certainly had their share of proprietary extensions to Java and SQL. At the end of the day, Oracle has always wanted people to write SQL. Sure they have Toplink, but it was never intended to allow true decoupling of one's domain model from its data store.
So now that Java has begun to embrace declarative and aspect oriented programming, shouldn't it be able to do something like RoR only better? One would think so. Of course high browed Java programmers (myself included!) wrinkle their noses at some of the shortcuts that RoR takes. Java is also chained to a legacy of interacting with legacy systems. For a long time it was Java's ability to interop that was a major selling point, but we're really past that now. Java 5.0 was definitely about giving developers the ability to do things quicker so they can compete with other technologies. J2EE 5.0 should be an even bigger step in that direction. This is all following what open source had already been providing. So now open source needs to go a step further and provide 'Java on Rails'.