Evidence is anecdotal, and a very clear cause like the Vietnam War is lacking.
But from surprising and diverse quarters one is hearing hostile sentiments aimed at America in general rather than simply at specific policies. George W. Bush is not the cause, after only four months in office. But he has perhaps been a catalyst, with actions ranging from environmental policies to missile defense stimulating latent anti-American viruses. Like any anti-ism, this is an emotional reaction rather than anything susceptible to reasoned discussion. But it needs to be recognized as a troubling trend.