Just stumbled on this today, and not seen it noted anywhere yet, but (recently?) Google has exposed its index of ‘Related Maps’ on Google Maps.
If you open the ‘Show Search Options’ option, there is an entry ‘Related Maps’ – this mainly seems to be GeoRSS feeds its found out in the wild, but does include maps from ‘My Maps’, but strangely not KML files (which are mostly indexed in User-Created Content I guess)
Oh and if you where wondering, yes did find this when checking something out on geograph. (Note the link at the top to view Related Maps)
Still waiting for the day when we get good access to Googles GeoIndex, the AJAX Search API gives very limited (32 results max, and no urls! oh and doesnt include all the options included in the ‘options’ dropdown on Google Maps either), feels so this data could/should be exposed more?