This seems very trivial, but during the in store activation in the Apple store, what exactly happens? Will they put my old SIM into the iPhone? I assume they take it out of the box (so I can't enjoy it myself ).
Yeah they take it out of the box and connect it to iTunes to activate it. Then they give it to you. If you plan on putting a screen protector on it, make sure you ask the person activating it to leave the factory film on it while he does this so you can peel it off and put the protector straight on for the best results. (or if you're at the Apple Store, employees there can put it on for you.)
There is no in-store activation this year.
...We'll help you complete your purchase, activate your new iPhone, and set it up for you.
According to the email I just received from Apple after pre-ordering,