I've been changing the DOCTYPE of most of this site to HTML5 recently, as generally there isn't too much else to alter in order to make it valid HTML5.
There are some elegant new semantic simplifications that HTML5 introduces. For instance, the header, footer and navigation elements of a site, are now defined explicitly in the HTML5 specification itself. So I'll be introducing them pretty soon here (this site is, in fact, only 4 seperate HTML pages)
I've had a few tiny niggles, nothing horrific, but annoyingly the 'last-modified' date fails validation using the W3C validator
From reading around various forums and blogs, it seems this is probably a 'feature' of the W3C validator, rather than a major problem with HTML5. I quote:
The validator checked your document with an experimental feature: HTML5 Conformance Checker.
I like that. 'Experimental feature'. Slick.
So we'll see, it is an emerging standard.