Is your site legal?
In many countries, it is illegal to discriminate against disabled people. Website owners have been successfully sued for publishing a site that was inaccessible to blind users. Employment and Human Rights law impose comparable requirements for Intranets. You may not be so constrained but it certainly doesn't hurt be accessible to all.
Is your site accessible?
Not only people with disabilities but potential customers using non-standard devices such as telephones and handsets need to be able to access your pages.
Is your site based on valid code?
Many designers use What You See Is What You Get editors to save time... these applications often create messy code that won't stand up to the error handling capabilities of modern browsers. Nor will their proprietary code validate to the standards of the World Web Consortium, which august body establishes these selfsame standards. So what? So your carefully designed web-site breaks in some customer windows.
Is your site standards-compliant?
As we come further out of the fog of makeshift HTML code and into the modern era of markup (the XHTML 1.2 Working Draft was recently released,) each iteration of the popular browsers and their parsing engines is less patient with sloppy code. It is the responsibility of us all (and to our benefit!) to foster ease of communication, and hew to a common standard.
