I love this plugin :-)
Everything works fine, except that... strangely enough, when I look at a map on my phone (Nokia C7, Symbian^3, screen size 640x360) the map (set as 300x300) does not display any visible placemark. The placemarks are visible when accessing the same page/ map from the desktop, both when using Firefox 5 and IE 9.
I don't think this is a problem with the phone browser, because if I tap on the link of the location (from the list of placemarks), I am forwarded to maps.google.com and the placemark is there.
I also went directly with my phone browser to maps.google.com and tried both the "mobile" and "classic" version. Placemarks are always visible...