WordPress.com introduced an entirely new range of retina compatible smilies few days back. They are bigger, better and beautiful. Self hosted users weren’t promised anything though there is an open ticket about introducing retina smilies but as of now its not going anywhere. But thanks to Janneke Van Dorpe who has released a plugin which will replace the default smilies with the ones wp.com is using. No change on your part is required. Just get the plugin from github and install it. And all your default smilies will be replaced by the new ones. No harm done.