I signed up for email alert for available phones for instore pickup earlier today, and just after an hour of signing up, I got a notification that the store closest to me (Tukwila, WA)has the Gold 5S 16GB AT&T, the one I wanted in stock, and sure enough, they did.
But I already have an order online, and I did not cancel the phone order I placed online beforehand, I knew that by the time my online order is canceled, and upgrade eligibility is cleared, the phone will be gone, so I didn't even bother to try. But I did watch how long it sells out: I got the notification of availability at 11:11, and the it's unavailable again at 11:34, so about 20 minutes, which is impressing.