Online shopping has made so many things so much easier. It's easy to forget that sometimes real, live humans are involved, behind the scenes! Currently, PDF ebooks purchased through Cooperative Press are added manually to your Ravelry library, by one of just a few very nice folks. They have to sleep, eat, and go to the bathroom like the rest of us, so it's not always instantaneous.
When you buy the print book + PDF combo (or just the PDF) through Cooperative Press's website, enter your Ravelry username in the space provided, and within 24 hours, someone at Cooperative Press will add Sock Architecture to your Ravelry library. If it's been more than 24 hours, you can email their support email address for help (that email address comes in your confirmation email and ends in zendesk.com).
P. S. - If you just want the PDF and not the paper book and have a (free) Ravelry account, you can buy it directly on Ravelry through this page: http://www.ravelry.com/patterns/sources/sock-architecture. I think, then, it IS just a computer on the other end, and it happens super-fast.
No matter how you get it, I hope you love it!