I have begun developing pages with the new HTML5 DOCTYPE:
<! DOCTYPE html>
This new DOCTYPE essentially puts the browser into a sorta "standards-based mode." Obviously this is all pretty new to most browsers but creating pages under this DOCTYPE will allow sites to last longer than ever. This also degrades gracefully within every browser I have tested in and no noticeable HTML or CSS downsides.
W3C has began using an experimental validator for HTML5 which can be used the exact same way as all of their other validation engines. An intersting side note: According to the W3C validator, you do not need to close the BODY or HTML tag at the end of the page; allowing for very minimal load time decreases.
As HTML5 continues to make its way to the forefront, I plan to begin implementing more advancements that just the DOCTYPE. For now that seems to be all that is new and widely supported.
Hope this helps.
-B
