I'm not a lawyer so don't take any of this as fact. Its not an attribution issue. Its more that if the data is mixed into the database in a certain way, that d

I'm not a lawyer so don't take any of this as fact. Its not an attribution issue. Its more that if the data is mixed into the database in a certain way, that data must also be made available under terms similar to the ODBl. So if I have the locations of the best Thai restaurants in a city, and I add this data to OpenStreetMap data, refine it based on the existing OSM data and present it, I must make my restaurant data available under the terms of the ODBl. If you are just overlaying data on top of image tiles generated from OSM data I think you are okay, but once you mix the data it becomes weird. For example if the OSM data has a few of those restaurants in it, and you modify your data set to remove them so there's no duplicates, I think thats a case where you must share your data back with the OSM project. You can check out the OSM (non-dev) mailing lists for more discussion on this.