Karl Groves in a post about HTML5, Longdesc and accessibility:
For nearly a dozen years now, I’ve been employed in a capacity which gives me a day-to-day glimpse of how professional web developers are using markup. I see HTML abuse on a daily basis. Bad HTML permeates the web due to ignorant developers and is exacerbated by shitty UI frameworks and terrible “tutorials” by popular bloggers. In my years as an accessibility consultant I’ve reviewed work on Fortune 100 websites and many of the Alexa top 1000. I’ve reviewed web-based applications of the largest software companies in the world. The abuse of markup is ubiquitous.
You should read the whole thing.