I'm a little skeptical of it; it seems very complex. In contrast, I'm leveraging the Ruby+RSpec infrastructure which I've already learned. And I interact with it via programming, instead of via configuration.

Also, by using just one language, Ruby, I can easily have full test coverage of the framework code itself. There are a lot of nagios plugins and scripts out there, but they don't seem to usually include tests of themselves.

But nagios is very intriguing - I'll check out what a "simple" install would be like.