The MediaGuardian 100 list is the definitive guide to the most powerful movers and shakers in one of the UK's most vibrant industries.This, the third year of its publication, has been the most controversial so far with the BBC director general, Greg Dyke, taking on the mantle of Rupert Murdoch as the UK's most powerful media executive.A panel of experienced media watchers gleaned from the worlds of politics, journalism, advertising and the internet judged entrants using three criteria: cultural influence, economic clout and political power.