Only reason I was there was because of the upgrade program.. this year you need to go to apply for the credit account/lease/whatever. Next year(s) you need to go to swap phones.
At Fair Oaks mall (Fairfax, VA, USA), it was very organized. Individual 'corral' lines for each reservation slot, we were checked in as we arrived (I got there at 0715 and was number five). At 0800, they took the first ten people and we were (of course) the first time for each person, so, it was fun. In total, 20 minutes in the store, five of which was her finding my phone in the back.
Note that they don't touch the new phone, it's activated by the new/current bar code scan, and you take it home and restore it, set it up as always. The whole credit check/application took about ten minutes and most of that was data entry on the little 5s (I assume) phone terminals they use. How quaint! (To quote a famous engineer...

).
In all, a very painless experience here. I've seen other stories where it wasn't so smooth...