Can anyone list some real examples of 'HTML5' being used in the wild?

I find these 2 sites to be good & practical examples of HTML5 usage -

• “20 Things I Learned about Browsers and the Web” is an online illustrated guide from Google aimed at casual users. There are plans to open-source the code.
• Stephen Walther's JavaScript Reference built with HTML5 & jQuery. The source code & explanation on how it was built is available from the author's blog.

The Stack Exchange network (of which this site is a member of) uses HTML5 for its authentication. That's why you can visit any site in the network and once you've logged in manually at least once, it will automagically log you in later.

Try it out - if you have membership on more than one site (say, here and Stack Overflow), clear all your cookies and temporary files. Then log in here, and then go to Stack Overflow and don't log in. Give it a few seconds and it will automatically log you in, even though the domains are totally different.