It describes how a site should be built upon a solid base , and then gradual layers of enhancement (Images, CSS, Flash, Ajax) applied to create as good an expirience as is possible for that user.
It used to be the case that screen resolution and IE or NS where the main factors, now there’s so many more options that need to accounted for. And if you want to provide a good user experience for more than the majority , you need to make the effort and do things right from the ground up.
At work we’ve done our best to work with progressive enhancement techniques, but it’s often difficult explaning to clients and even designers how and why this is important.
In a commercial situation progressive enhancement is a tricky beast, it doesn’t fit well with how many web design agencies work. There are few practices (thatI know of) to help with this challenge.
I hope this article will go some way towards improving peoples understanding of the situation.
Aaron has managed to sum up my philosophy towards web design much more succinctly and clearly than I have been able to.
So I urge you to read this article, I know i’ll be telling friends and collegues to do the same.