All -
Although I haven’t been using JRuby much recently, I’ve found that in
the
absence of a native 1.8 install, JRuby is really handy for comparing
1.8
and 1.9 behaviors. I just needed to do this for a gem that uses colons
in
case statements, which is no longer permitted as of 1.9:
https://github.com/sspinc/confluencer/issues/1
I just wanted to point this out because it’s a use of JRuby that may not
be
readily apparent.
[Bow to Charlie, Tom, …]…of course, this is just a microscopic
fragment
of the value of JRuby. 
- Keith