We have been using a Progressive Enhancement approach much more in relation to our web work. In a nutshell, this means we provide a good looking site on all browsers, then on more modern browsers, we use features that let us stay even closer to our designers' designs. So while we might not be able to show rounded corners to users of IE8, we can still provide meaningful content and a site that looks good and save the fancy features for browsers that do support them.
And the illustration. Don't miss the illustration.
Nerdy, relevant stuff as the number of browser versions continues to grow. And if none of this makes sense, this little cartoon poem may do the trick.
Read the whole article on the Click Rain Blog: On Progressive Enhancement, Responsive Design, and IE