A year ago or so, we added a Google Map to a website friends of me are running. The website is about reptiles and amphibians. In one part of the site users can enter details into a form, including the location, when they’ve seen an interesting species. In the meantime their database has grown to a comprehensive collection of (crowd sourced) information like species distribution among our country. It’s not only a hobbyist project, the database means quite a valuable input for species research and protection projects too.
Anyways, before we added a Google Map to the form, user provided location information was very poor. Only a rough location description or coordinate information based on the national topographical map were possible to enter. For national coordinates users had to go to another website, look up the place and copy and paste the coordinates from there back into the form. Definitely not what I would call a convenient solution.
Once we added Google Maps where users could simply pinpoint the location on a map, the collected data turned into something like this:

Green dots … located with Google Maps (92%)
Red dots … located with a service of our National Mapping Agency (8%)
That says something about the benefit of public available mapping APIs. Especially for projects like this, with no commercial but a strong public interest.
Ordnance Survey heads into a good direction by releasing OpenSpace. OpenSpace is a mapping API, based on public geodata and OpenLayers, the Open Source JavaScript library for mapping. OS is probably the most progressive European mapping agency, so there is hope that others will follow (once they have all fulfilled INSPIRE and are done with metadata updates). It took some time until maps showed up at public authorities’ websites, followed by interactive maps and nowadays you even find WMS here and there. The next evolutionary step is probably public geodata made available through APIs.
During the INSPIRE process it became pretty clear that European mapping agencies don’t favor free public geodata. The API concept could help here: it enables flexible usage of data for users while retaining full control over both, functionality and data, for the mapping agency. Seems like a workable compromise to me.