Ian Bicking's interesting and provocative blog post on HTML Accessibility is a good read. Empirical accessibility is a good idea. I think by this he means making it work for real users. Fred Brooks' ideas about the computer scientist as toolsmith seem very relevant.
I've been thinking about grass-roots accessibility for a while, though I can't say I've made much progress. It seems to me we have to somehow empower people to enhance accessibility in a bottom up way without much help from developers.