When the middle-class in America was booming, you would have had to be crazy to leave America. Good job. Nice car. Family and a house? You're set! Why leave?
Another way of viewing what has happened in the US over the past 20 years or so, is that the US middle-class is falling back to earth. Now the average middle-class family in America could move to just about anywhere in Europe and enjoy a pretty similar lifestyle to what they currently have in the US. Sure, gas is still more expensive and clothing is still a bit pricy, but it's nothing like it was in the 80s and early 90s. (I still remember seeing electric razors advertised for the equivalent of $150 on my first trip to Germany when the equivalent model in the US would've cost no more than $50.)
Take that one step further, and the average American family could now potentially consider a move to one of the BRIC or CIVITS nations, and they would find themselves with only slightly less access to the luxuries they might expect in the US.
Why is this important? Because I think that for the first time in the history of human kind, we might just be reaching the point where the choice of where to live and work could be made based solely on things like the climate or the culture instead of on things like "Can I eat?" or "Will I have a roof over my head?"
That would be a world I would want to live in...