feature: flexbox status: use tags: none flexible kind: css
Go for it! CSS Tricks' A Complete Guide to Flexbox provides strong reference documentation for all properties and values, and Dive into Flexbox is a good overview of the spec. Additionally, the flexbox docs at MDN are excellent and the Putting Flexbox into Practice slide deck shares a practical path of using flexbox today.
Flexbox has a funny history: the flexbox spec changed significantly through three major revisions (Chris Coyier shares how to tell which flexbox you're looking at). The current version is now a W3C Candidate Recommendation and is stable.
Browser support: The new spec is now implemented in all 5 major desktop browsers. On mobile, the old spec is in Android browser 2.1 and Firefox Mobile, and the new spec is in iOS Mobile Safari 7, Chrome, Opera Mobile and Blackberry. There are presently no robust polyfills for the current spec, however you can mix old and new flexbox for maximum browser support.