HTML5 Development

HTML5 is catching attention of many people and companies lately.
Heck, even Microsoft is shifting it's rich client technologies to HTML5...
It's going to take some time until HTML5 will be the mainstream of web development but until then, why not prepare yourself? That's at least my state of mind :)

So here some questions that popup:
Are there any IDEs which already support these new features?
Best practices? TODO/not-TODO
What websites already adopt HTML5 technologies (other than just the