Assuming you’re eligible for an upgrade straight away, it looks like you can only order an iPhone 4S for delivery on October 14 — you can’t reserve one for pickup at your local store. So if you (like me) enjoy standing in line and hanging out with your other nerd pals, it’ll mean (a) you have to get there sooner than normal; and (b) if you aren’t towards the front of the line you may end up getting a size or color you didn’t exactly want. Or: (c) you can decide this’ll be a year you don’t stand in line for an iPhone.
It’s interesting (and slightly annoying?) the way Apple is always fiddling with different launch-day ordering tactics.