While I don't have the links to the articles, I do know that Brian Marick is contemplating writing a book on using Ruby for testing purposes. (This comes from his posts on the SW-Test mailing list.) My guess is that the articles mentioned previously are also authored by Brian.
And a side note, there is another thread going on on that mailing list discussing favorite scripting tools.
I've just started using Ruby myself, and as a tester can see how I might create a test harness with Ruby. I doubt I'd use it to perform testing of other apps as that's not what it's designed for. For more questions about Ruby, check out http://ruby.weblogs.com/ and the home page of Ruby http://www.ruby-lang.org/
Christopher A Walters
Security/Performance/Software Architect email@example.com