"[T]he usual 30% capacity use was actually more like 50% in gusty 2003." So says the British Wind Energy Association in the BBC article linked to in this post's title. The U.K. Department of Trade and Industry, however, has reported that the output of on-shore wind turbines in 2003 was only 24.1%.
The developers hire whole teams who work full time keeping the misinformation going, while their opponents have to counter it in their spare time. Still, we have the advantage: There's a lot more of us, and we're not liars.