No idea why the proof of purchase wasn't an upload to your Asus account
Instead of full mailboxes and the added difficulty of tying in proof of purchases to the registered Nexus 7's in people's Asus accounts, why didn't they just let you upload the proof of purchase from within your Asus account? I guess this would have required some coding/validation, which they decided they couldn't do in a timely manner.
I did eventually send off my proof of purchase this evening (and it didn't bounce - yay!), but I'm not hugely optimistic about the whole thing - it seems to have been a shambles throughout:
* No obvious indication that it's for 16GB Nexus 7 owners only (which happens to also rule out the Google Play 8GB purchasers).
* Incorrect screenshot w.r.t. the serial number - the 16-digit one (that's in the Settings page) is the wrong one. It's the 12-digit one on the cardboard box and it *is* hard to distinguish 0, O and D's before you ask!
* After putting in the serial number, date of purchase and the retailer you got it from, you've still got to e-mail proof of purchase, even though they've probably already got enough info to verify your purchase.
* E-mailing the purchase proof to Asus was bouncing back throughout the weekend, which was simply poor planning on their part.Iit was deadly obvious that you'd have PDF/screenshots/HTML flying into their inbox at a rate of knots, so to not prepare for this was a double facepalm moment.