HTML 5 is here with much deserved fanfare and attention. Before cracking open a book and putting HTML 5 elements all over your website, you need to consider who your users are and you site purpose. The main groups of website and web application users are below.
Company Intranet – Internet Explorer Only
However, you can still use the fantastic new form elements (email, number, website etc) and they will render normally in IE6. Use the new HTML doctype header (<!DOCTYPE HTML>) at the top. IE 6 will assume it’s a HTML 4 header and other HTML 5 enabled browsers will recognise it.
The new ARIA roles are also compatible with IE 6, which is great.
Public Website – Modern and mobile browser oriented, obsolete browser users not important
For further info on using HTML 5, there is a brilliant video from an HTML 5 author at http://vimeo.com/15755349