You could either give your form and input control an id (then refer to it using document.getElementById("formId:controlId").value = xxx), or alternatively you could use Seam Remoting to call a method that persists the values.

I have just been doing the same thing. I have a draggable marker on the map that I have added event listeners to...

marker = new GMarker(point, {draggable: true});
gmap.addOverlay(marker);

function showDetailBalloon() {
    marker.openInfoWindowHtml(address);
}

function closeInfoBalloon() {	
  gmap.closeInfoWindow();
}

function assignPoint() {	
  document.getElementById('addressForm:latitude').setAttribute('value',this.getPoint().lat());	
  document.getElementById('addressForm:longitude').setAttribute('value',this.getPoint().lng());
  var remotePoint = Seam.Component.newInstance("geoPoint");
  remotePoint.setLatitude(this.getPoint().lat());
  remotePoint.setLongitude(this.getPoint().lng());

  Seam.Remoting.getContext().setConversationId("#{conversation.id}");
  Seam.Component.getInstance("addressRemoteAction").setLocation(remotePoint);
}
						
GEvent.addListener(marker, 'click', showDetailBalloon);
GEvent.addListener(marker, 'dragstart', closeInfoBalloon);
GEvent.addListener(marker, 'dragend', assignPoint);

Mainly derived from Dan Allen's article, and the Google API's. It updates the input fields whenever the marker is released, and then on a subsequent form update, saves those to the database. However, I was really wanting to update the coords via @WebRemote interfaces. The above sends off the information as displayed in the Seam debugger, and the target session bean gets hit, but the geoPoint coords are missing from the geoPoint object on the server side. So yet to work out why that is, but I suspect I may have an idea. However, I have the fall back with the web form for saving the data if I cannot find the solution.

So it sounds like I am about where you are, but I am able to save my coords to the database from the input fields, whereas for some reason, you are not? So I thought I would share with you my approach so that you could potentially see if there was any difference and perhaps resolve your issue.

Cheers.

Andy