Context sensitivity is a great justification for hidden elements. Litter your page with visible edit buttons and, in a poorly designed UI, you might forget what part of the page each edit button binds to.
It makes sense to show only some controls when your mouse or cursor is focussed in the right place, because then you know those controls are relevant to what you're doing.
What I think was overlooked with the two examples - Github and google - is the replacement of text-based controls with icon-based ones. Github's top nav is now just tiny icons, the Google pages are all icons. You can barely tell what these are unless you hover over them long enough to see an explanation. This is the real problem, I think.
Comments
Context sensitivity is a great justification for hidden elements. Litter your page with visible edit buttons and, in a poorly designed UI, you might forget what part of the page each edit button binds to.
It makes sense to show only some controls when your mouse or cursor is focussed in the right place, because then you know those controls are relevant to what you're doing.
What I think was overlooked with the two examples - Github and google - is the replacement of text-based controls with icon-based ones. Github's top nav is now just tiny icons, the Google pages are all icons. You can barely tell what these are unless you hover over them long enough to see an explanation. This is the real problem, I think.