Simply add placeholder="foo" to your input element, and that's it:
Compare this to the old way as explained in the previous post:
Unfortunately similar to other new HTML5 specs, the support for this is still limited.
Specifically the lack of IE support could be a problem for anyone wanting to support the majority of browsers. The importance of usability, especially with labels of forms is extremely important. I would suggest using Modernizr or a similar library, combined with the two techniques above. This will ensure that users with modern browsers get the fastest experience, while stragglers still get a similar experience.