It probably uses the power from the VGA or DVI signals to turn the relay on again.

Sure, the PSU can be turned off, but I'd be interested to find out how the signal is detected - does it complete a circuit, or does it need a circuit that sits there monitoring it (in which case power, and thus zero watts, is required..)

Take a look at that sign. The background is just plain green behind the "0." What's up with that, some last minute editing from when they finally found they could cut it down to 0 watts consumed?

My monitor is powered from the 12v rail from my PSU.
Also didn't the old macs that came with a proprietary video connector (ADC) do this as well (DVI + 24ish volts for power)

Isn't there a few more cost-effective ways to do this?

1. Push the button on the monitor when you leave for the day.
2. Have the janitor shut down power to the floor at night.
3. Hook-up a relay between the usb port and the monitor power cable, so the monitor only gets power when the computer is on (and the usb has power).

Why does the "0" look like it's been photoshopped?

And at at least 120 quid more expensive than any other decent 20 inch LCD it will only take 20 years to pay itself off in energy savings!

Various manufacturers released transistors aa well as small chips to run things on mircoamps on standby many many years ago already, and they cost a few pennies, so this is a bit late and not that impressive, and I hope that panel justifies the price because putting in a 4 cent transistor does not.
And seeing how it's in fact easy and cheap to make a next-to-zero standby and the industry had ages to start using it but didn't really one wonders why the EU and such haven't stepped in yet, if you see where they did step in it's a bit curious how they skipped this.

This is complete bulls**t. Let's say that you have a monitor that draws 1,5 W in stand-by. With a little math we find out that if the monitor remains in stand-by an average of 20 hours a day it draws 20 h * 1,5 W * 365 = 10,95 kWh per year. For the sake of simplicity let's assume a price of 0,1 Eurocents per kWh. We get a grand total of 1,1 saved Euros per year. In the end you pay a lot more for this 0 W monitor than you would for the wasted energy.