Progressive Enhancement is

Everyone has a definition for progressive enhancement these days, and many often misunderstand the concept. I like Scott Jehl’s thoughts on the principle:

Progressive Enhancement is less “but what if JavaScript is disabled?”, more “can our core services be more tolerant of everyday conditions”

When you look at it that way, progressive enhancement becomes synonymous with quality. Why wouldn’t you want to build sites and applications this way? In a way that gives people a quality experience no matter what.