Brandon Satrom (a developer evangelist here at Microsoft) has a great article on HTML5. It's a very detailed oriented piece that explains what HTML5 is, the interaction between it and Internet Explorer (IE) as well as the Microsoft developer tools that are supporting it. Brandon further describes Microsoft's approach to the new standard, and helps you think about how to adopt HTML5 technologies.

Actually this is the first of a series of articles that aims to show you how you can use HTML5 to build apps for the web so I’ll be sure to update this post when his upcoming articles are published.