A couple weeks ago I gave the monthly presentation at the Tucson JUG on the programming language Clojure. Only six JUG members showed up but they were very interested in the language and kept me talking for over an hour beyond my initially allotted hour.
There are many reasons why Clojure has really caught on in the last year or so. For me, it's a well-designed and pragmatic amalgam of Lisp, concurrent techniques, and functional programming built on the JVM. It also helps that there's a great book, a friendly and helpful community, and dozens of enthusiastic side projects.
My slides (as a PDF file) are available in the Tucson JUG's Google group area:
Note that my presentation relied on material from the Clojure community, including the website, forums, and the terrific book "Programming Clojure" by Stuart Halloway.