You can monitor your memory usage/leaking with System.totalMemory property. This way you can see how memory is used, where leaks are and you can optimize those parts that are eating too much memory.
In simple words use System.totalMemory as bellow (in KB):
var memoryUsedInKb:Number= Number(System.totalMemory/1024).toFixed(2);
I used it to show the used memory in different units: bytes, Kilobytes, [...]