These rack servers are busy soaking in a bath of mineral oil, using natural convection to carry away heat. This is totally different from the oil that the McDonalds fries are cooked in. This oil is non conductive allowing working electronics to soak in the oil and keep cool. This is a good trick to keep your CPU cool when you are over-clocking, although liquid Helium is even more effective, you start with liquid Nitrogen and then switch to the liquid Helium and you can cool to extremely low temperatures. This posting talks about a world record; cooling a CPU and achieving 8.429 GHZ with an AMD CPU. Here is a link with some more information about mineral oil cooling: http://www.engadget.com/2012/09/05/intel-servers-mineral-oil-cooling/. This is a good way to keep the machine cool, although you have quite a job cleaning your carpet if you have a spill. But if you built a sturdy perspex box like a fish tank; then the tank would be very strong and would be safe to use. If you had a coiled pipe in the tank with the motherboard and it contained very cold water that was circulated by a pump through some kind of refrigeration system then the oil could be kept cool. Just using a tank of oil on its own would slowly get hotter as the oil heated up and would take a very long time to cool down again. There is a nice water cooling guide here: http://forums.extremeoverclocking.com/t176597.html. This contains many useful links and information to help you get started with liquid cooling. The old Cray-2 super-computer was liquid cooled. It used an inert liquid to cool the circuits.
The point of overclocking your CPU is to obviously gain speed and make a world record, especially if you are using liquid nitrogen and then the liquid Helium to cool to extremely cold temperatures. If you ran the computer on the surface of the Saturnian moon Titan you would get even better cooling, but that will not be a possibility for a long time yet. How long will it be until we see a 10 Gigahertz CPU overclocking attempt? With the overclocking comes the risk of damaging your CPU with the heat and driving it far faster than it is supposed to be, outside the parameters of the design. The old Intel Celeron Cpus had incredible overclocking ability and this is still continuing, but with overclocking far faster than we could have dreamt of back then. But a modern CPU has a good level of performance compared to the old days of computing. We used to think that a 486 DX4/100 was a beastly machine. Or a Pentium 4 with a 3.06 Gigahertz CPU. Now we have dual-core CPUs in mobile telephones. That means a mobile Android phone can be as powerful as a desktop computer. The future of computing will be very interesting, the power of devices will increase; but the size will get smaller and smaller. The move to the tablet interface has created the Ubuntu Unity interface and the horrid Windows 8 Metro abomination has resulted in Microsoft creating the strange Surface laptop, which is just a tablet with a keyboard attached.