Openstreetmap lacks an easy way to create mash ups for the non-technical user. This is why GoogleMaps is much more popular among those users. This wiki page is mend to keep track of my idea's (and yours) around this subject. This page is currently without any structure. But maybe that will come some day....
I think the best approach is to use Dynamic KML. Especially since dynamic kml (for the mash up data) could then be read into other apps.
- An API has to be written so people can submit new data to the mash up.
- The possibility to use multiple mashups when displaying it in openlayers.
- Multiple mashups per users