I remember in school very often people would form their groups, usually based on social class, life philosophy and race/nationality.
I look at the development community and am somewhat reminded of high school. Every time people find out that i am an American working for a European organization they are usually surprised and working in a European organization i very rarely run into Americans. Now i never hear (perhaps because i am American but i don't think so) oh i don't hang out with Americans or hear Americans say they don't' hang out with Europeans and indeed i can think of many exceptions but in general, i seem to see Europeans at parties, restaurants, etc hanging out with each other and the same for Americans... disturbing.
In job hunting i have discovered that many of the "beltway bandit" organizations pay better than average European (and American for that matter) organizations but the disturbing part to me is that i see this separation even more in people who work for these organizations.