Many people say developing in Python, Ruby, PHP ...etc is much faster than Java. 
Question is, why? In terms of coding, IDEs, available libraries... etc. Or is the speed in making the first prototype only?
I'm interested in answers from people who worked long time on Java and long time on other languages.
Note: I have developed for .Net before Java and yes it was faster to make some apps, but on the long run (large web projects) it will become like Java.
For rapid prototyping the more dynamic the language the better.  Something like excel is a good for rapid prototyping. You can have a formula and a graph with a dozen clicks.
However in the long run you may need to migrate your system to something more enterprise friendly.  This doesn't always mean you should start this way.
Even if you start in Java you may find you want to migrate some of your code to C for performance reasons.
What makes other languages faster than Java in terms of Rapid Development?