Recently my team has been trying to find ways to help streamline our UX Design workflow, which now is some combination of sketching, Illustrator, Axure and HTML prototypes. With the release of Illustrator CC, we have started taking advantage of some of the new functionality and improvments, namely converting some of our style guide design elements into dynamic, reusable elements.
Utilizing the appearance panel, we can dynamically create buttons that retain their style without having to manipulate the elements to fit the specified text. I've created an Ai file that has buttons from the Flat UI toolkit, Bootstrap 3.0 and some custom Social buttons using Font-Awesome. Use these however you see fit, hopefully they'll be useful.