Facebook contributes an estimated £2.2bn to UK GDP

"Facebook estimates that it benefits the UK to the tune of more than £2bn a year, including the development of an almost £500m "app economy" that has sprung up around the world's most popular social networking website.
The company commissioned a study by Deloitte, which concluded that Facebook supports 35,200 UK jobs and fuels £2.2bn to UK GDP each year, and published the document at the DLD conference in Munich on Tuesday.
Deloitte's estimates looked at the direct economic impact of Facebook – such as paying tax, profits and wages – as well as the more broad impact it has had in enabling businesses to reach customers, make sales, create and monetise apps and even boost demand for products such as broadband and smartphones."

Source:  The Guardian, 24th January 2012