The new airport express seems to do everything the airport extremes do just with less ports at half the price. Since I just purchased a rMBP I was looking to potentially hook up an external HDD on the network to save some stuff. I don't really know too much about this but I do know you need an USB port which the express has but says its only for a printer whereas the extreme has only one USB port as well but says it could do both. Any help or suggestions is greatly appreciated.