Any given Flex application will probably use many labels to display information. The only downside is that you often want the value (test) assigned to the label to be formatted a certain way without having to parse your input each time, assign it to your a label's text property, then style the label as needed. All of this can be done by extending the label itself which gives you a customized label component that can be re-used throughout your application either as a simple label or as an ItemRenderer within a DataGrid.

For Example:

<?xml version="1.0" encoding="utf-8"?>
<mx:Label xmlns:mx="http://www.adobe.com/2006/mxml" creationComplete="init()">
    <mx:Script>
        <![CDATA[            
            private const POSITIVE_COLOR:uint = 0x000000; // Black
            private const NEGATIVE_COLOR:uint = 0xCC0000; // Red
           
            private function init():void {
                if(this.listData != null) {
                    this.text = data[this.listData["dataField"]];
                }
            }
            override public function set text(value:String):void {
                if(value.match(/^-?d+.?d*$/)) {
                    var amount:Number = Number(value);
                    var str:String = "$";
                    if(Math.abs(amount) < 1000) {
                        str += amount;
                    } else if(Math.abs(amount) < 1000000) {
                        str += int((amount / 1000)*100) / 100;
                        str += "k";
                    } else if(Math.abs(amount) < 1000000000) {
                        str += int((amount / 1000000)*100) / 100;
                        str += "m";
                    } else {
                        str += int((amount / 1000000000)*10) / 10;
                        str += "bn";
                    }
                    super.text = str;                
                    setStyle("color", (amount < 0) ? NEGATIVE_COLOR : POSITIVE_COLOR);
                } else {
                    super.text = value;
                }
            }
        ]]>
    </mx:Script>
</mx:Label>