A lot of guys have mentioned about the heating/cooling costs...
I think that if they had designed the building properly, then it should be alright... heating is a bit of a problem since all that hot air rises to the top and you need to constantly supply heat from the bottom. One solution is to circulate the interior air, rather than constantly reheating the bottom, colder air. Three corners of wall (as oppose to fully glass) would lessen the heat loss effect too. There are many other solutions to keep the costs down as well. But yeah of course it still wouldn't beat a standard one-storey building.
You might think that the computers inside would contribute to the heating, but actually the environment is considered a large enough heat sink so the effect is negligible
Oh well, too much engineering studying.
The large surface area of glass gives plenty of light inside, though I hope they have actually tested that if the sun constantly heats up the screens of iMacs, the screen would actually turn black (like burnt). It has happened to my iMac once and the screen was super hot, luckily it turned back to normal.