I tried to get this plugin to work without a google API key and to use the OSM layout. No Joy. When I went and got a Google API v3 key (which are retro actively good for v2 of the API) then the OSM would show up. However, I was trying to get my NextGen Gallery images to show up on the map and there was no joy there. It is supposed to be automatic with the [xmlgm ....] shortcode.
The author says this plugin is end of life due to a lack of time. It would be nice if the Google code portion were updated to v3 of their API (as google suggests) but also because version three of the API does not require an API Key.
I was really hopeful that this plugin would work for mapping my NextGen Gallery images.