The video learning site "lynda" has a really good set of videos on this: "Web Accessibility Principles" and "Improving SEO Using Accessibility Techniques." Ess

The video learning site "lynda" has a really good set of videos on this: "Web Accessibility Principles" and "Improving SEO Using Accessibility Techniques." Essentially they teach you to build web-sites for disabled users and at the same time for search engines. The gist is that search engines really ARE disabled themselves, they're somewhat blind and dumb. So you really start to think about how information is presented on your site for more than just the fully-able users and when you look at "tricks" like putting labels within the placeholder element you immediately/instinctively know it is going to cause problems (for SEO and disabled users alike). Worth checking out if you're interested in this topic and have a "lynda" account.