Yeah, I feel the same way. It's a little tougher for me because I'm buying mine outright so I either have to get the T-Mobile phone from Apple and hope it's unlocked or order an AT&T phone through their website.
If I can't get either then I'll head out to the AT&T store early next Friday morning.
So if your pre-order doesn't work you're not completely out of luck.
I want a 6+ in 128GB, prefer space grey since I already bought a case. I'm expecting those to be near impossible to find on launch day so I'm really hoping I can get one tonight. If I do then I have take next Friday off so I can sit here waiting for delivery even though it'll probably be the last delivery of the night.
Pre-order sucks though, I tried it once, for the 4 I believe, and it was hours or trying to load the website. Then you get in, get part way through ordering, and it won't load. Just know that you're in for a rough time tonight.