Just released today is a new WordPress Plugin: RICG Responsive Images. I think this is the start of kind of a big deal.
Important I-got-it-wrong addendum: it works everywhere, automagically! See Tim Evko's tweet. That is seriously amazing and a big deal.
I know that some people aren't very fond of WordPress. Static site generators are all the rage these days. WP is not as light as Jekyll and it's not as cool as Wintersmith (or whatever tiny static generator is the new hotness). I still use WordPress for this site (although I do use Jekyll for a bunch of other stuff).
The thing is that WP has a very low barrier to entry, so lots and lots of people use it ("WordPress powers 23% of the internet" according to WordPress.com today.). You don't have to know how to code to get a site up and running, and pick a Theme and play with the design. That's pretty awesome.
The plugin let's you hardcode srcset-powered responsive images in to a template. That means that, for now, only Template authors can really use it, and only for images in the template (not for content images). This is still a big deal though, and the start of something awesome: the roll out of responsive images to a lot more of the web. Huzzah!