Found some really useful code samples at Diving into HTML5.  They make liberal use of Modernizr (easy way to detect browser capabilties)

Coding for a particular feature boils down to:

in HTML head

<script src='modernizr.min.js'></script>

and then wherever you want:

if (Modernizr.feature) { supported }

Very easy to code and use.

You need to generate Modernizr with the features you care about.  (That’s a little odd – why not just do everything?)

Have detection page coded at http://www.dantoomeysoftware.com/html5/html5.html