From David Crow: Website Accessibility in the Private Sector:

Ronald Milliman at Western Kentucky University has published a study analyzing private sector web sites for accessiblity. His results showed that 98.24% of the sites sampled failed the Bobby accessibility test for ADA Section 508 compatibility. The most interesting findings are that web designers were not knowledgeable of the exact techniques for making their site fully compliant (17.40% were knowledgeable) and that web designers did not feel that disabled users were a part of their target audience (42.07%).