I'm now able to answer my own question and provide info to others.
I've just returned from the Aspen Grove, Colorado store, which apparently had one of the longest, if not the longest queues early on of any store in the state (I got there at 1AM and there were 55 already queued ahead of me, many of them sleeping in their cars all morning with the engine running).
You would think that this store would have a lot of stock for walk ins, but it didn't.
They had good supply of AT&T which was good for me as that's what I was after. Most of those ahead of me when they started handing out reservations to return and pick up product were buying the maximum # of phones in groups, asking Apple lots of questions about where phones would work and buying Verizon phones.
With about 30 ahead of me they reported that all 256Gb Verizon Silver were gone. Shortly after that they reported that all Verizon were gone.
Someone behind me indicated that many of those up front were scalpers purchasing phones for resale in countries like China, Vietnam, etc... this might explain why you would often see one person shepherding a larger group around.
Anyways, when they got to me, number 56 or so in the queue, they were down to AT&T, some T-Mobile and a couple of Sprint models and that was it.
There were only another 30-40 people behind me but the total size of the queue was still around 100.
The stock levels appeared to be pretty low for at least Verizon. The maximum # of Verizon phones they could possibly have had was less than 100.
Obviously different stores have different inventory levels. This is a fairly busy store but inventory levels weren't fantastic. I do know that Apple flagship stores tend to have very large numbers of phones where-as the smaller stores might only have a handful.
In some launch party threads it was being reported that Apple was coming out around 5-6AM and telling those who waited overnight that there was no stock for walk-ins and that they only had stock for existing reservations.
Somewhat shocking if true.