Rails has been a major ingredient to our success. I'd almost like our use of Rails kept quiet, but when all your developer job postings have "RoR" in them, it's not a very good secret. :)
We've been very lucky to be able to borrow from a wealth of talented developers, documentation, innovative open source projects, etc. Of course other languages have tremendous communities too, but Rails really fits us well. Rails and Ruby have gone a long way in helping us try to create simple, fast, and stable solutions to our customers' needs.
And of course as Rails evolves, they help us evolve. We've got some really cool stuff coming in 2009 that is made so much easier to get done because of this framework.
Hope everyone has a wonderful holiday and Happy New Year!