Am 80% of the way through rebuilding a website with a responsive design at the moment. The one thing that can be time consuming when you start switching the site over is that the images and videos don’t change size to suit your new layout.
If you’ve got a lot of videos on your site, rather than having to go through the whole site, using a jQuery plugin called FitVids is a life saving moment as it resizes all the videos from YouTube and Vimeo for you and makes them responsive too. I can’t recommend this enough. For more info visit fitvidsjs.com.