I had the same problems. But I've got it almost running now. I used the 2.4 API and edited the estateagent.php like below
// $gmap = new GoogleMapAPI('map'

;
// $gmap->setAPIKey($ea_gmap_key);
// $gmap->setWidth($ea_gmap_width);
// $gmap->setHeight($ea_gmap_height);
// $gmap->setMapType($ea_gmap_type);
// // string $address the map address to mark (street/city/state/zip)
// $gmap->addMarkerByAddress($address,"GMap Test","GMap Description"

;
to:
//NOTE! Depending on where you live this will be different! This works for sweden, figure out how your country has it!
$address = "$obj->street $obj->streetnr $obj->pcoce $obj->town $obj->country";
require($mosConfig_absolute_path."/components/com_estateagent/includes/GMapAPI.class.new.php"

;
$gmap = new GoogleMapAPI('map'

;
$gmap->setAPIKey($ea_gmap_key);
$gmap->setWidth($ea_gmap_width);
$gmap->setHeight($ea_gmap_height);
$gmap->setMapType($ea_gmap_type);
//string $address the map address to mark (street/city/state/zip)
$gmap->addMarkerByAddress($address, "<strong>Go here</strong><br>now!!"

;
//$gmap->setCenterCoords($lat,$lon);
$VDloc1=17.618550;
$VDloc2=59.855620;
$gmap->setCenterCoords($VDloc1,$VDloc2);
I edited the coordinates.
So far so good. At least at this stage I have a map and a marker. But when I try to put in the next code as in the beginning of this thread the map goes blank. So the marker isnt centered in the map. I have to be close now. Anyone willing to help me out here?