Here's a way to add a scale bar to the map.

1) Customize portal_skins/qPloneGoogleMaps/maps_markers

2) Add after line 43 or so:

    if controls == 'large': sControls += "map1.addControl(new GScaleControl (), new GControlPosition(G_ANCHOR_BOTTOM_LEFT, new GSize(10, 10)));\n"

This is a hack: is there a more elegant and thorough method?

Not NOW,

maybe the next version of product will allow a higher level of maps customization. Maybe some configlet with maps configuration.