From a CBC Interview with Malcolm Gladwell (thanks to Glen for the tip), this thought on the socioeconomic effects of emigration:

Immigrants have complex relationships to their places of origin. By virtue of leaving a country, an immigrant changes not just the country they come to, but they change the country they leave. We always talk about how immigrants change the country they go to; that we can see. We forget that it’s true about their place of origin. By virtue of their absence they leave a mark. If you think about Jamaica, who left Jamaica? Enormous numbers of middle-class people, my family among them. We altered Jamaica, and not necessarily for the better, by leaving. Jamaica lost its educated, its professional class – huge numbers of them – to Miami, Toronto, New York, and London.

Substitute “Spain” for “Jamaica”, and add cities like Berlin, Munich, and Amsterdam, and the same pattern still holds today. When large numbers of those with the drive and the ability to leave do so, what kind of society do they leave behind?