The namespaces, class names, and the architecture of the v3 API changed completely from the v2 API. I wouldn't call an upgrade hard, but it's not trivial. Further reading: Announcing Google Maps API v3.
You do not need an API key for the v3 API anymore. Simply include the script you mentioned in the question.
Geocoding an address on hover is not very difficult. You may want to check out the following example to help you getting started:
Example:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
<title>Google Maps Geocoding On Hover</title>
<script src="http://maps.google.com/maps/api/js?sensor=false"
type="text/javascript"></script>
</head>
<body>
<div id="map" style="width: 400px; height: 300px;"></div>
<ul>
<li><a href="#" onmouseover="gc(this);">Oxford Street, London, UK</a></li>
<li><a href="#" onmouseover="gc(this);">5th Ave, New York, USA</a></li>
<li><a href="#" onmouseover="gc(this);">Via Nazionale, Rome, Italy</a></li>
<li><a href="#" onmouseover="gc(this);">Rue de Rivoli, Paris, France</a></li>
</ul>
<script type="text/javascript">
var address = 'London, UK';
var map = new google.maps.Map(document.getElementById('map'), {
mapTypeId: google.maps.MapTypeId.ROADMAP,
center: new google.maps.LatLng(40.71, -74.00),
zoom: 13
});
var geocoder = new google.maps.Geocoder();
var marker;
function gc(element) {
geocoder.geocode({
'address': element.innerHTML
},
function(results, status) {
if(status == google.maps.GeocoderStatus.OK) {
// Clear the previous marker
if (marker) marker.setMap(null);
// Set the new marker
marker = new google.maps.Marker({
position: results[0].geometry.location,
map: map
});
// Center the map on the geocoded result
map.setCenter(results[0].geometry.location);
}
});
}
</script>
</body>
</html>
Screenshot:
