Author of another CSS regression testing tool here which doesn't depend on your full web app being up and running (which is the default for WebDriver and friends).
I'd be seriously interested in feedback from people who have run a CSS regression test suite against a deployed web app, and especially how maintainable their testing setup was a year in and how much defects it found in that process.
My personal experience with WebDriver for acceptance tests have made me approach such things very carefully. I am very conservative in how much I want to leverage a full stack setup.