We changed ours in the Fall of 2014. Make sure your plumber and DC water coordinate schedules. DC water only changes the line until the curb and then you have to pay for the rest. It cost about $2500-3000.
They need to shut the water down on the street so it's helpful if you give your neighbors a heads up. Once, it's done you need to use filtered water for drinking and cooking (including washing veggies) for six months. DC water gives you filters and pitcher. They then test six months after the lead line replacement. While the results came back within the acceptable level, since I was pregnant we opted to put in a water treatment system for our kitchen sink.
Hope that helps, Alexis