Placed order at about 10:20 AM, email came through a few minutes later for creating a password on the tesla site. I created it, then got an email with a confirmation. Not sure if creating it spurred the confirmation, I think not and the confirmation would have come anyway. But then I was able to log into my account and see my reservation number.
Granted, I got lucky and was able to do it in Italy in person for a US delivery because I'm traveling. So the system traffic was low since the US stores hadn't opened yet.