Use coordinatePoint() instead of locationPoint()

You probably won't notice the difference if there's only one marker on the map, but if you're planning on ever putting lots on at the same time you should convert the latitude and longitude to an MM.Coordinate in the constructor and update the position using map.coordinatePoint():

// in the constructor:
me.location = new MM.Location(latitude, longitude);
me.coord = me.map.locationCoordinate(me.location);

// in updatePosition:
var point = me.map.coordinatePoint(me.coord);

This will be much quicker because conversions between map and screen coordinates is linear.

Also, I would suggest putting the popup's DOM node into the marker so you don't have to update its position separately. :)

Start by reading the marker constructor and updatePosition method in the JavaScript implementation, focusing on the current locationPoint() usage. Verify that the location becomes an MM.Coordinate once and that updates use map.coordinatePoint(); done means marker positioning follows this path, with the popup DOM-node suggestion assessed separately.