Using the "Remote objects under dRuby" example here: 
http://www.ruby-doc.org/stdlib/libdoc/drb/rdoc/classes/DRb.html
Following it, exactly.

But it freezes when it tries to call this line:
logger.log("Hello, world!")
Everything works until that point.

This same freeze happens with 
http://pragmaticprogrammer.com/titles/ruby/code/smp670.html

What they all have in common is DRb::DRbUndumped - so I'm guessing
that's the problem.

I'm running Ruby 1.8.2 on different/remote computers to do this test
(client names server by IP address.)

It works when I run both on the same computer, but as soon as I try to
put client and server on different computers, it seems unable to use
objects passed by reference.

NOTE where it froze, above.  It's able to pass the object by
reference.  It receives it back on the client.  But when the client
tries to use it, that's when it freezes.

I've tried this on various FreeBSD and Mac OS X computers, at home and
work, without firewalls.  All other DRb code works fine except when
using DRbUndumped.

Any suggestions?