For those interested: I'm working in this field, doing some datacenter stuff (buildings, cooling, power, not the stuff IN the racks, I'm a utility guy, not an IT person

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http://erdsjb.free.fr/PureStorage/Provi ... oogle2.jpg
Definitely NOT the best use of space, in spite of Google's comment. Look at the large pathways, and the amount of vertical space wasted. I frankly don't understand the cooling concept on that image. It might be a cold isle, but what's all that stuff doing on top of the racks? Could be the same center as image number 6.
http://erdsjb.free.fr/PureStorage/Provi ... oogle4.jpg
This one I've seen before. Nice use of colors for the different sections of piping. Makes identifying easier. I just love how much space Google has to setup their datacenters. The ones I'm involved with are typically much smaller, and have way less space...
http://erdsjb.free.fr/PureStorage/Provi ... oogle5.jpg
Custom Google boards. Those colors are only added for marketing purposes.
http://erdsjb.free.fr/PureStorage/Provi ... ogle6..jpg
This picture is more interesting. All those mini fans are probably mounted on the back of the custom Google main boards, ie. if a board fails, or a fain fails, then swap the whole board. If there were single, large fans behind you would not be able to replace that specific fan (too dangerous in there). The flexible tubes going up are probably hot and cold flex piping, ie. cold water towards the top mounted heat exchanger, and warm water out again. The steel structure could be improved a bit to allow engineers easier access to the piping and exchangers.
http://erdsjb.free.fr/PureStorage/Provi ... oogle7.jpg
This picture is less clear, but I suspect hot isle / cold isle separation using those plastic flaps. If that isn't a raised floor (the image would suggest it isn't) I guess that's in-row cooling in the image above.
http://erdsjb.free.fr/PureStorage/Provi ... ogle10.jpg
Just a water tank, typically used to buffer water for a few minutes in case there is a power loss and the chillers need to restart on generators. Largish, but not really special.