Just a word of caution: Try not to put more than 3 and maybe 4 rigs on one outlet. And that is only if they are straight WCG only rigs. 3 machines with 500watt psu's is 1500w and that is close to the max for one circuit.
Bear in mind there will almost certainly be other outlets on the same circuit.
If you run each rig under load and measure the power draw with a kill-a-watt meter and you're sure that you're not anywhere close to the PSU's max output, then of course, plan accordingly. But in any event, make sure you know what other appliances are on the same circuit and what their draw is.
One german power socket should be able to hold out 230V x16A maximum, for a short time equalling in about 3600W available.
If its used continously, the power should not exceed 2400-2800W, then it should be in the safe range.
That depends on which kind of fuse and powerlines are used. ordinary power lines and fuses are built for 16A today, some older are for 10A. (our house is a newbuilt one though)
Some buildings have thicker power lines, and use 25A Fuses, which equals in somewhat 5700W maximum, and probably around 4500-5000W continous draw.
thanks for the warning tho, in the first moment i was shocked, when i calculated that i should already draw more than 2200W max,from 2 sockets of the same circuit, when every PSU is on its peak use
(which luckily no one of them is till now, but the 600w OCZ in my main rig maybe will be soon
)