A US traveller has written to point out that Ethiopian Birr are essentially worthless outside of Ethiopia!
They say “When we arrived at the airport in Addis Ababa, we converted several hundred U.S. dollars to Birr. When we arrived at the airport to leave, we tried to convert our remaining Birr back to U.S. dollars. The currency exchange office at the airport told us that we could not convert more that the equivalent of $150.00 per person from Birr back into dollars. When we originally converted our U.S. dollars to Birr, the currency exchange office did not tell us about this limit. When we got home, we couldn’t find any place in the Washington, D.C. area that would convert Birr to U.S. dollars.”
The same would be true in most places outside of Ethiopia, so the moral of the story is not to change too much currency when you first arrive. Bear in mind if you change too little money, it is now easy to change more money at almost any bank, or to draw local currency from ATMs using a Visa card.