One thing that I make use of but don't see too many services providing is some kind of 'match level' - where the geocoder returns a code indicating how confident it is about the quality of it's result. A result of 1 might mean a building level match, while 100 might be street level etc.
IIRC Google's geocoder does something like this, but it's pretty inaccurate, overstating it's match level consistently.
As others have said, geocoding is very hard to do well, but I commend the efforts being made with Nominatim and komoot/photon.
The problem with the iframe approach is that Google's geocoding service TOS explicitly states that the output of the geocode operation can only be displayed on a Google map.
Google's geocoding service is underpinned by a lot of third party datasets which would have to be (very expensively) relicensed if Google started passing the results out to maps under the control of other organisations.
Not quite retail, but Amazon's main Data Centre in Dublin is the former main warehouse used by one of Ireland's largest retailers. It's gone from being full of beans and nappies to servers full of kitten gifs.
I believe that other transport modes (public transport, on foot) are in the pipeline, but the amount of additional compute power they need is significant
Also Public Transport route and connectivity information is frequently a bit patchy in OSM, but this is steadily improving.
However putting a non-existent island on a Marine chart used for navigation is a few steps above that. It looks like it's the result of a mistake, a mistake that was copied far and wide.
I'll add the obligatory tip of the hat to www.openstreetmap.org - it's community basis and the ease of use of it's editing tools make this kind of issue very easy for users to fix.
And as a bonus, any edits you make to the data aren't owned and copyrighted by a large corporate, but are made available to everyone via a Creative Commons Licence (soon to be ODbL)
IIRC Google's geocoder does something like this, but it's pretty inaccurate, overstating it's match level consistently.
As others have said, geocoding is very hard to do well, but I commend the efforts being made with Nominatim and komoot/photon.