Here's a quick list just off the top of my head: * YellowPages.com * All of the 37signals apps (Basecamp, Campfire, etc.) * Hulu * Scribd * LivingSocial * Penny Arcade * GitHub * Twitter (backend powered by a ton of stuff but their frontend is mostly Rails) * Chow.com * Oracle.Mix * Shopify * Justin.tv * Crunchbase There are a ton more public facing and even more (as you mention) sort of "behind the firewall" type stuff. Ruby (especially Rails) has stepped up as a pretty major contender in the web development arena.
Yes, let's all have a good laugh at my surname. I picked it out myself after all. I kid. I get that a lot.
Looks like the stock is getting slim over on Amazon, so if you want to order it still and they're out, hit up the Manning site: http://manning.com/mcanally/ Thanks!