We use Ruby to implement our test automation software. This includes test framework and driver code for Selenium RC, WATIR and AutoIT.
Ruby is powerful enough to create comprehensive applications that can interface with Test tools like Selenium or WATIR, while at the same time reading from data files, interacting with a remote Windows UI and performing near transparent network communication. All while running on Windows or Linux.
The uncluttered syntax makes it ideal for new and inexperienced programmers to read. While its totally OO nature makes it easy for these same programmers to apply good (recently learned) OO techniques, from the start.
The flexible nature of Ruby's syntax also makes the use and creation of DSLs much easier. This allows less-technical people to get invovled, read and possibly create there own tests.