Want Google without the input field?
plus.google.com
plus.google.com
Furthermore, are other sites able to use this feature as well?
I'm personally worried that the current trend of browsers deviating far from a "standard" look will create problems for those who are not as prone to tinkering as we are. For them, things seemingly disappear and (re-?)appear at random and apart from the back button and the address bar there's really not much in the way of consistency anymore.
Even Explorer windows in Windows do this by hiding the menu bar unless you press Alt. It's not intuitive; "our kind" is very much an exception with our ability to find these things after the fact.
Presentation mode (pictured in article) hide away all window chrome for... presentation
(worst ever? the full screen functionality change in OS X Mountain Lion for those of us with more than one monitor: it blanks the second monitor for apps that uses the OS provided mechanism for full screen - at least some apps now "fake it" to avoid pissing off users).
Although its all of a sudden introduced this nasty bug: It steals focus away from the address bar which is horrible.