That one thing, RoR, isn't the best option at all today.

The moment that XHttpRequest came to be - it started the countdown to RoR's popularity decline. HTML5 just made it permanent.

ruby does a lot of things well - it is still the best language i've found for quickly exploring a problem in code, or prototyping a solution. i'm less happy with the experience of maintaining a large codebase in it but only because i've found other languages that have much better support for that.