Last night Charles Oliver Nutter, one of the leads of the JRuby project, gave a 2+ hour talk on Ruby, JRuby, and JRuby on Rails to the Gateway Java User's Group (JUG) in St Louis. According to the report on his blog, it was a resounding success, with over 50 excited attendees.
It was a great experiment for me to do this presentation, primarily because it was one long demo. There were a few slides to bridge things together, but ultimately I spent two hours typing into IRB, vi, and bash to demonstrate Ruby, JRuby, and building and running a simple JRuby on Rails app. There were a few glitches (I forgot a few metaprogramming methods, and my new migration initially failed because I ran it on an already-migrated database) but I managed to recover from everything and get all my demos across. I think the live walkthroughs coupled with a very enthusiastic and interactive crowd made a fun presentation for folks in attendance.
Alex Miller from BEA captured a fairly long transcript of the walkthroughs including code samples. Charles himself has made his slides available at the following links: Gateway JUG JRuby Presentation (Opendoc) and Gateway JUG JRuby Presentation (PDF).