Graceful Degradation & Progressive Enhancement - Accessites.org
Accessites.org has a good discussion on Graceful Degradation & Progressive Enhancement
Progressive Enhancement
Progressive enhancement became known — at least under that name — in 2003, when Steve Champeon began using it on Webmonkey and during the SXSW conference. It starts at the opposite end from graceful degradation: begin with the basic version, then add enhancements for those who can handle them. Again, comparing it to the design approaches: this is the same basic thought as in structural design. That starts with the markup and adds styling on top of that, which is progressive enhancement all by itself.