[altano]

If flex hasn't completely changed how you write layout related CSS, and it isn't because of legacy browser support, you're missing out.

I also recommend this guide which is very visual and helped me a lot: http://css-tricks.com/snippets/css/a-guide-to-flexbox/

[tomphoolery]

What's browser compatibility like on this? Do I need to install any polyfills to get this to work on older browsers (mostly older IEs)?

[billsossoon]

http://caniuse.com/#feat=flexbox

Internet Explorer, as usual, screws everything up. No support in IE8 and IE9, limited support in IE10.

[altano]

In practice, IE10 is totally fine. If you have to support IE9 and lower you shouldn't adopt flex box yet.