I finally got the demo to download! If you've already gotten to the stage where you could hit download after going through the GOW:A countdown page, but then got an error, you should be able to go into your account via the XMB and then download the demo from your download list. At least that's what worked for me.
It should slowly start working for most I think now.
Unfortunately I don't have the capabilities for any decent gameplay recording, but go here if you wanna watch live footage!!!
It's already started, but only a minute or so in!