As the NY Times recounts:
A memo explaining the policy change, from the company’s human resources
department, says face-to-face interaction among employees fosters a more
collaborative culture — a hallmark of Google’s approach to its
business.
In my experience the answer is a bit of yes and no. First of all Yahoo seems in my opinion to be a dying entity, just is no one seems to have told the patient. But that aside, it is nice to have key people accessible, but that can be accomplished in various ways. But again leadership is essential, if you demand certain performance from your troops you must be out in front doing ten times more. If you do not lead by example then people immediately see you as a self centered egoist. Not a good thing when you are trying to right a sinking ship.
The other side of this argument is that if you want people in the Office then when they are away from the Office the corollary is that you leave them alone; no cell phone calls, no emails, no video conferences, no instant messages, no nothing. Yet I suppose that this side of the equation will not be honored.
Productivity can be quite high "at home" or not in the Office. I can be ten time more productive. Yet my group productivity demands face to face contact, not even a video conference makes it. So I travel to Boston, Washington, etc to "meet" people since effective collaboration is contact intensive. Thus one must separate the two functions; collaboration versus concentration. Programmers, writers, etc may function better alone and at "home". Executives must meet, but then again they are on the road frequently.
Bottom Line: It all depends and no one size fits all. But again one leads by example. I spent a portion of my life doing "turn arounds" and that demands up front leadership, leadership that has people follow, not be ordered to do so.