Matt May of Bestkungfu and a little group called the W3C has written an article for Digital Web called Accessibility From The Ground Up. It's a 'primer for the web designer' (his words, not mine) that runs through the various things that designers need to get up to speed on. I have to agree with Matt's comment here:

The hardest part of Web accessibility, in my opinion, is the stuff between the angle brackets. You get your content from a dozen different sources, often with a dozen different voices. Some of it, like legal text, is irreducible. Changing it even slightly could alter it dramatically, if you were even allowed to do so.

So true. Once you have a basic understanding of how to make a page accessible it becomes second nature, just something you do without thinking (a state of mind some would describe as being 'unconsciously competent' ... yes, I've been on a training course!). Cutting out legal text and marketing nonsense, now there's the real challenge!