Behat is really useful. I've recently been on a project where we are using it extensively and I don't see myself not including it in every project going forward from here.
I came across a situation that behat couldn't handle out of the box and had to write my first step. The scenario was checking an XML element for a given value. I found that the WebDriver we were using did not handle XML. Some do, some don't. The one we're using didn't.