I am looking at HTML5 information at W3. Some of the new functionality seems interesting.
Which browsers support it?
How can I ensure that I am using HTML 5?
Is there a way to be told that "there is an HTML 5 command you should be using" if I use something in HTML 4 or what not?
HTML 5 Canvas is supposed to allow a lot of Flash type functionality no?
The best guide to HTML5 compatibility I have found (by a mile) is this: http://a.deveria.com/caniuse/#agents=All&eras=All&cats=HTML5&statuses=rec
A general info and other resources can be found here: http://prezi.com/vo2ommkmkl_w/
AFAIK, webkit-based (safari, chrome, etc.), firefox, opera, and IE 8 support some, not all, of the HTML 5 features. Things like video are inconsistent as Apple/Webkit want H264, which mozilla is against (they prefer ogg or something) because of licensing issues.
Use feature detection and the HTML5 doctype. I'm not well read, but you can read up some here.
Canvas is supported by all browsers -- except IE, but Google provides excanvas to allow IE to support canvas (it's slower than a native implementation). Canvas provides a location to directly draw on the screen.
For some examples of canvas usage see processing.js and Bespin. Canvas is definitely capable for drawing at a decent speed, excluding the useless IE.
There's information in the WHATWG spec itself, look for the browser icons in the boxes to the left of each sections. And there's the Wikipedia page, which should be quite up to date (disclaimer: I do a lot of the maintenance there).
Which browsers support it?
HTML isn’t one thing. Different browsers support different parts of it.
Mark Pilgrim’s Dive into HTML5 is a good reference.
How can I ensure that I am using HTML 5?