If you haven't sent out your Christmas cards yet, you might want to get on it, quick. Snail mail just got slower. The cash-strapped U.S. Postal Service announced Monday that it's going to end next-day delivery of letters, postcards and other First Class mail. The agency is looking to find $20 billion in annual savings by 2015, about $3 billion of which could come from various plans to shrink the network. But what will become of the letter?