OVER 9000 MARKERS! 100K, to be specific.

Reload with markers.
Be careful, 10M takes about 500MB of RAM and usually kills browser. 1M should be fine.
Place mouse over marker to see amount of markers inside.

Code

            
var random = [];
for(var i = 0; i < 100000; i+=1) {
    random.push({
        latitude: 180*Math.random() - 90,
        longitude: 360*Math.random() - 180
    });
}

$("#map1").gMap({
    markers: random,
    zoom: 1,
    latitude: 0.1,
    longitude: 0.1,
    clustering: true,
    fastClustering: true,
    clusterSize: 40
});