I’ve spent the past few hours reading about HTML5. I was also able to convert my current blog design to HTML5 and CSS3. It’s interesting, and was actually rather fast – but I think I’ll stick with XHTML 1.0 and CSS 2.1 at the moment. I was able to find a fix to make the new HTML5 elements work in IE, but when I tried using CSS3, things started to get messy in IE.
Reading about it was interesting, though. The new elements like <nav> and <time> can make the markup easier to understand – especially for beginners. It was a little confusing at the beginning, though. I also think the <header> element is a bit unnecessary, especially when used with <hgroup> . Aren’t all the headings – h1 to h6 – already semantic?
I guess the only thing stopping me from using HTML5 and CSS3 is the fact that about 40% of my blog’s viewers still use IE6 (switch to Firefox or Opera, people!). I guess it’s enough that I’ve learned about it, like reading about best diet pills. Maybe we’ll be able to use HTML5 and CSS3 in 3-4 years – but we’ll probably still hate IE (cross browser compatibility, you are the bane of my – blogging and professional – existence). 
If you want to know more about HTML5, here are some useful links: