According to Mr. Rails himself, Amazon is getting in on the Rails fever.
UnSpun is a Rails application that relies heavily on the Amazon Mechanical Turk Web Services. It allows you to "see the community consensus on what's the best or the worst, the scariest or the funniest, the tastiest or the dumbest, UnSpun provides the right amount of structure to make that possible". Once a list is created, its sent to the Amazon Mechanical Turk which helps get the list populated with items, as well as the most relevant web links for the items.
Perhaps Amazon chose Rails because Ruby is the best programming language, or maybe because it's #5 on the Best Model View Controller Frameworks list, or maybe because its #194 on the Most Promising New Technologies list, or maybe because ActiveRecord is the Best ORM Layer?
Whatever the reason, it's interesting to see a company like Amazon embrace Rails. Maybe one of these days I'll get around to building something in Rails, brand it as Web 4.0 and rake in a cool billion?