This site is lovingly-crafted using CSS3 and a smattering of XHTML. I did start off with that thar new-fangled HTML5 malarkey, but my web server kept interfering. Whilst HTML5 isn’t yet a standard, all decent browsers support it (Safari, Chrome, Firefox et al). If you want to know more about HTML5, then I recommend (most effusively), Dive into HTML5 originally from Mark Pilgrim, now maintained by others.
I try to be mobile-friendly courtesy of some CSS3 media queries trickery, which re-arranges the bits for your more cramped viewing pleasure.