* HTML5 is a multi-vendor effort; browser vendors in the HTML WG
* Focus on Web apps, new document semantics too
* Support existing content: a browser implementing HTML5 can consume legacy content using the HTML5 rules.
* Degrade gracefully: new HTML5 features don't break the whole page in browsers already deployed.
* Don't deploy new markup or scripting features before you have browser that implements those features to test with.
* Off-the-shelf parsers dramatically lower the cost of consuming HTML. _You_ can now parse HTML with a real parser and not just regexp hacks.
* HTML5 is already being implemented piecemeal: (examples from Firefox3 / Safari 3.1 / Opera 9.5 / IE8)
* You can use pieces of HTML5 a long time before REC.
* You can participate.
* Seeking to bring MathML and SVG to text/html (in progress)