good article on business week on retaining talent. http://www.businessweek.com/magazine/content/05_41/b3954001.htm
They use Schlumberger as the primary example for good practices in encouraging a global workforce. I have worked with SLB for a long time and I have been truly impressed with the quality of the management and their diversity. It is one of those rare companies where international assignments are not only encouraged but also a requisite element of moving up the chain.