Last year(2008) about $300 billion dollars moved around the world by wage earners sending it home to their families. Africa saw $20 billion in remittances, compared to $18 billion in direct investment and $25 billion from official development aid.
This doesn’t count all the people who stuffed it in an envelope, because the risk of theft outweighed the cost of sending it securely. The average amount sent via Western Union is $250-300.
Below are stats on what every person should know about how the “remittance economy” (AKA western union and money-gram money transfer services) affect the world, and Africa in particular: