Progressive Enhancement is a web development methodology that not only allows greater portability and accessibility but in my opinion, makes the development process easier.
What I want is to know what the rest of the community think of this approach.
In particular: What do you believe is the minimum set of technologies that a web application should support?
If it remains usable in a text-only browser (without CSS and Javascript, of course) and also in a screen-reader, you're on the right track. But these are about the highest standards that you'll find :)