Christoph Stöpel has a couple of cool webpages: Geogen and Lokator. English translations are forthcoming, but it's said that the Geogen maps are based on data from recent versions of German telephone directories.
Geogen is returning some interesting results for the surnames I've searched, namely that some of them no longer exist. I'm not sure if that means the names have died off, if the records need to be reexamined to validate the believed spelling or if the name evolved into an alternate spelling, but I did utter "uh oh" a couple of times the other day. Less shocking and rather pleasing were results that showed some of the names are still concentrated in districts where the families lived as far back as the 18th century.