As responsive design grow in popularity, I'm seeing some incredible implementations of responsive done right. And with clients without a specific mobile site, we're seeing a marked improvement in search engine visibility as well.
WordPress themes have adopted the strategy and there are some incredible examples out there (our agency site is one of them). While the design and stylesheets are complex, the great advantage is not having to maintain a specific look and feel in multiple areas, or through a plugin. We hope to eventually make Martech Zone responsive one day!
Here are some advantages to purchasing a Responsive theme for your next WordPress implementation from the folks at WP Responsive Themes: