Yesterday Microsoft released an update to Visual Studio 2010 to implement a much improved HTML5 & CSS3 support. You can download the Web Standards update from the Visual Studio Gallery and enjoy the new features immediately. I downloaded it last night and I am already feeling the improvements as I work this morning. I am not going to get into a detailed review, but rather point you to some of the ASP.NET team members blogs for more details. But the update lets you designate HTML5 & CSS3 as the validation rules for files, removing newer tags from appearing as errors or warnings. It also adds some intellisense support for newer tags and properties.
So go download, install and start creating your awesome web applications!!