HTML 5 intellisense and validation schema for Visual Studio 2008 and Visual Web Developer is for downloading. Follow the instructions posted on the page to install the new scheme. Seems like the Visual Studio Team will be supporting HTML 5 after all.
How can you support something that doesn't exist? Something you can't validate against because there's no accepted spec?
Yes they could build in support for the experimental DTD, but they did that with XML/XSLT/XPath and ended up fragmenting XML support for far too long and were attacked for it from all sides.