Jon's quick summary of Java scripting languages

BeanShell
:) zero learning curve for Java developers
:-( can't create classes

JRuby
:) concise regular-expression handling
:-( can't shortcut .getFoo() to .foo
:-( can't concatenate strings and numbers directly

Groovy
:) concise regular-expression handling
:-( filename must be valid class name
:-( can't use Java prior to 1.4

Jython
:) whitespace defines blocks - concise
:-( creates a bunch of *$py.class files
:-( no boolean type
:-( can't concatenate strings and numbers directly