React is a game-changer, and will fundamentally change the way we build apps on the web. To learn more about it, here are some great resouces:
Pete Hunt gives a talk introducing React at JSConf EU 2013. slides
A blog post by Pete Hunt which explains the basics of React components.
Great walkthrough on how to create fast animations on modern mobile devices.
Fun proof-of-concept where Rails TurboLinks is married with React with some mind-bending results.
Take the red pill, and check out Om, which is the combination of ClojureScript with its immutable data structures, and React. This is where things get really exciting! (Follow David Nolen for more interesting tidbits.)