The service was retired on April 17th due to low use and a misalignment with what the service was named and the actual data it delivered. The data delivered was a ratio of the estimated daytime population to nighttime population???in other words, you had to do your own math to get an actual estimate of daytime population. There is no replacement.Here's the ArcGIS Online Services life cycle status document:http://downloads2.esri.com/support/product%20life%20cycle/online_gis/ArcGISOnlineServ_PLC.pdfThanks,Mike