“As you can see, you can do some pretty bad things with JavaScript that will certainly drive your visitors away (or insane!). So why is this kind of functionality available? Some functions is actually very useful if you’re writing complex HTML5 web applications. By disabling text-selection on interface elements you can make the application easier to use, and you can re-implement the right click menu using your own options.”
1stwebdesigner: 20 snippets you should be using from HTML5 Boilerplate
Sounds stupid and listy but it's actually a good introduction to some of the more useful and practical pieces of the huge insane HTML5 Boilerplate (html5boilerplate.com).