I'm on a roll here; this is one of those great days when you get paid, solve customer problems, and get featured in important places on the Web. Let me quote.
From the World Wide Web Consortium Q&A blog, article titled Craft of HTML:
HTML is a practical art. In a professional context, it requires precise and extensive skills. As with many popular crafts, the vast majority of people do it on their own, but only a few do it for a living. The quality of products varies a lot.
Bruno Pedro has recently published Top blogs fail W3C Markup Validation. He has taken the top 20 list of popular weblogs and puts them through W3C validator. None passed markup validation. Then the author is encouraging people to take care of validation. The comments following the article express either frustration, anger or support. This article is a good illustration of the misunderstanding about HTML validation.
When you are a developer of a content management system, of an authoring tool, of a small widget, be sure to create all the fonction to sanitize the content in production and input. Maintaining the quality of your content is a better goal than a one time validation.
Reference of tools
Incidentally, I validated my own pages and I found two validation issues related to the Creative Commons license (something about the XML namespace used by the code) so I just commented those stanzas out. Dear Lazyweb, how can I specify several valid namespaces for an XHTML document?
To the W3C staff: thanks :-). Much appreciated.