Here's my experience:
My wife and I got to the AT&T store this afternoon and pre-ordered two 16GB iPhones. Total with tax was $208.xx per phone (5% VA sales tax, on the subsidized price).
While our very attentive sales rep was entering the information I said "So I read online that the pre-orders here don't actually mean you're going to definitely get the phone on day one, right?" He said that basically the store stocks have not been determined yet, but what he has been told is that anyone who pre-orders will have their phone waiting for them at the AT&T store for pickup that day. Beyond that, they'll have some kind of arbitrary number (he said 50, but was just using that as an example) to provide to others who had not pre-ordered.
He seemed rather well-informed, and was rather adamant that we'd have our phones on launch day. He also mentioned that this particular store did not have set plans for an early launch. He said there would definitely be something, but they just need to finalize everything with scheduling and whatnot. So from what it sounds like, and what I experienced, going in to an AT&T store is a very painless way to get things done if you want two new iPhones on a family plan!
Big thanks to Sergio from AT&T for being a great CSR.
So what I'm understanding, after reading this thread, is Direct Fulfillment orders (which our two phones are) will ship with our names on them directly to the store, on our behalf. The fact that we've ordered so early (one day after the announcement) means that we have a quite high chance of our phones getting to the store on the 19th. Hope so!