You can now add the HTML 5 intellisense to your Visual Studio 2010 and 2008, it can be found over at this URL:
To make sure the HTML 5 Intellisense is works correctly follow the instructions at:
Once you set the HTML 5 switch, then it works, but there are documented issues such as:
HTML 5 intellisense and validation schema is experimental and has certain limitations. For example, VS and VWD (both 2008 and 2010)are not able to validate ‘wildcard’ attribute names, like HTML 5 data-* attributes and is not able to handle ‘transparent’ content model when element content is defined by the element parent (see, for example, A element). However, it may help you to start playing with the new standard.