This site lets you pick a year and see how far we have come towards the still un-official HTML5 specification:
http://html5readiness.com/
It 'says' we are very compliant with some browsers - but I cannot say if I have noticed if any of my favorite websites have upgraded to requiring HTML5.
I suspect millions of sites have not upgraded due to the cost of re-development and the concept that the new browsers are backwards compatible to HTML3/4.