Calling Java in Rails (JRuby, jrb, yajb) - real-world experience?

Hi,

I'd be interested to hear from people who have used either JRuby or one
of the Java-Ruby bridges like jrb or yajb to call out to Java classes
from Rails.

Which bridge did you use, how did it work out? Which one do you
recommend?

Is anybody running Rails on JRuby on a production server, or is Rails
on JRuby still to experimental for that?

Thanking you in advance,
Elmar