(Via Jeremy Miller)
WATIR was the first thing that ever made me interested enough to install Ruby. The idea is great; browser-based testing of your web site. You write scripts that drive the browser. When the main output of your software development process is a web site, any tools that allow you to run automated tests are at a premium.
The only thing that made me break stride was Ruby. Sure enough - I like playing with new languages, but it was a disappointment to learn that I'd have to learn yet another to get the benefit. Anyway - your customer doesn't want to hear that you're planning to add yet another hot skill to the training requirements for the team.
But now, there's Watin. All the same good stuff as Watir, but you can write your scripts in C#. I'm itching to have a go.