It started changing in the mid-90s. There was lots of talk about American financial imperialism (I was living in London at the time). When Tony Blair joined forces with Bush to go into Iraq (when the British parliament had voted against it, and the majoirty UK population didn't want it), America lost status even faster.

I've lived in three European countries since (Spain, Germany, and currenlty Portugal), and there is not a high opinion of the States. It is seen as the country most likely to cause WWIII.