I've heard about contracting companies that talk people into getting work visas and then will send people over even though they might not be the most qualified, and when people get here, usually alone, they are trapped and can't switch companies and also miss home. I'm not sure about the economic component, but at the ground level I've heard pretty bad stories (granted not the end of the world), and the primary winners are the large companies that have large supplies of cheap labor, while all of that could be avoided if they took the time to properly sponsor someone or just hire locally.