There is a certain style of button on the latest YouTube design (most easily found in the footer) where the default state of the button has a very subtle bevel to it, but on :hover and :focus states the button pops up, eager to be clicked.
This design works well in the context of YouTube's footer. The default state is very subdued, meaning these buttons aren't competing for attention on a site where almost everything else is. You still get the very rich/obvious experience of pushing a button. They imply a different functionality than the other links in the footer (press these, and something will happen, press a link, be taken away to another page). They make good on that implication as well, each of those buttons opens up a panel of settings right beneath.