Does anyone have some real-world Airport Extreme usage feedback they can share? I am especially interested in the Airport Disk feature. Any suggestions on the best external hard drives to use for this purpose? I know that some drives power-down after a period of inactivity, and I'm really wanting to avoid having to re-mount the drive to the network repeatedly throughout the day. Please note whether you are happy with your purchase or if you think it's overpriced for the current features offered. Thanks.