var teasers = ["It's loading, don't touch that mouse.", "Still loading", "Almost there!", "Done and dusted."];
var started = false;

function onSourceDownloadProgressChanged(sender, eventArgs) {
    sender.findName("uxStatus").Text = "Loading: " + Math.round(eventArgs.progress * 100) + "%";
    sender.findName("uxProgressBar").Width = eventArgs.progress * 500;

    sender.findName("TeaserText").Text = teasers[Math.round(eventArgs.progress * 3)];

    if (!started) {
        sender.findName("BallDrop").begin();
        started = true;
    }
}