If people actually spend time on your site, they would be wasting it, as your data will not carry over to OSM based datasets, unless you spend more time converting the data into usable format for OSM. In which case, they probably should have been using http://www.openstreetmap.org/ to draw to begin with.
OSM is rightfully skeptical of uploads. Even when cities give specific permission to OSM, it's up to the community whether a large import is helpful or risks drowning out local mappers. If anything, this site would be helpful to download a subset of the city's buildings as KML and use JOSM to upload.
This site exists as a custom mapmaker. It's easier for a non-GIS user to get data out and make custom maps compared to OSM APIs and tiles.
I've recommended it to a non-technical family member (he's a realtor) and they were able to create and host their own kml-based maps within an hour's time. Note that it does not use polygon based building markers, but rather addresses (and coordinates), which are simpler for non-GIS people to use.