This is an interesting question for me. I just finished 3 major Java EE projects. One was an existing J2EE project and was kept that way. But the year before I did a Java EE 5 project (2005-2006) and it was a much easier to implement due to improvements in Java EE. I redid that application in 2009-2010 (6 months) in Java EE 6 with a lot less effort and much easier to maintain.
So why would I care about Ruby on Rails 3? There are lots of reasons. Mostly it is intellectual curiosity. Another is that I am not a one-size-fits-all kind of guy. So I am kicking back and reading a great tutorial by Hartl and finding the new Rails is much easier to pick up than when I first tried version 1. I have skimmed a number of Ruby books and from my background with Flavors and CLOS in Lisp and Smalltalk I find Ruby pleasing. I am not a big fan of all the type checking in Java but it has some good points. Then I picked up on a book on metaprogramming in Ruby and bingo, the ability to do things at runtime that I loved in Lisp are back. The book is Metaprogramming Ruby: Program Like the Ruby Pros by Paolo Perrotta. This book has really accelerated my understanding of to use Ruby and just how some of the great gems work.