For people who are on the iPad color and size selection and have no "continue" button on the right or whatever it's called, just wait or refresh your page...it's up to you.
It WILL show up, it just needs to load that button after you've made your selection...given how the site is getting hammered right now, it will take some time. What I did was let that page load and let it sit for a bit. Then when I selected black/32, the "continue" button showed up instantly.
For anyone who doesn't have a card on file with their account, I recommend opening up iTunes and adding your card through the store. That's what I just did, because I've never purchased anything off the Apple Store.
Boom just got my confirmation email...about 12 minutes, if my timing is right.
If I have time, I will try to try again and see if colors load for the smart covers. But yeah - for now, during the selection process, let the page load a bit. Give it some time. I'll be around for a bit to try and help out.