As you can see from the following graph the hype around Ruby on Rails is beginning to fade:
What you see in that graph I pulled off Google Trends is a plot of "Ruby on Rails" in blue verus Django in red. I put in Django just for reference, the important point is that Rails peaked somewhere in the middle of 2006 and is now declining.
Not only is the 'popularity' of Rails declining we are already starting to see the rise of a backlash. The backlash isn't surprising in the technology arena, particularly involving something as 'religious' as programming languages.
All of that should not diminish Rails, but instead should put it in proper persepective. The real value in Rails was a singular, opinionated vision of how web developement should be done. That vision moved the bar for the whole industry, which is quite an accomplishment. But there's nothing magical about Ruby, or Rails. All of the underlying concepts of Rails can be 'ported' to almost any other language, which is exactly what were seeing today, with Rails-like frameworks appearing in Python, Perl, etc. Rails success was defining the platonic solid for second generation web frameworks. Framework 2.0.
Just like I don't believe that there will be a 'next Java' I don't believe there will be a 'next web framework'. There's plenty of room for lots of second generation web frameworks.
Just so I can save some people the trouble of sending me hate mail: