Know your numbers' is a fundamental precept of business.

Creating a piece of software is always complicated because you're doing something new. If you just wanted something that had been done before you'd just use that old piece of software. So there are no repetitive tasks.

Skype actually does get a fair bit of revenue.

I think given all the different imperatives - getting energy to Africa, security of energy, climate change, that we should be spending half as much as we spend on health, which will get you all the way up to $15 billion - the health people don't like it when things get compared to their number.

It's energy intensification, where we essentially have, through our light bulbs and cars, the manpower of [hundreds of] people working on our behalf, helping our food being created, helping our materials like steel and plastic and wood and paper be created. Our lifestyles are incredibly energy intense.

The finest pieces of software are those where one individual has a complete sense of exactly how the program works. To have that, you have to really love the program and concentrate on keeping it simple, to an incredible degree.

Our vision, which has not changed since the day the company was founded.