Re: My Nexus 7
"I know seven days is a hell of a lot better than you get for the non-Nexus devices, but it was frustrating not knowing when it was going to be my turn, others in the UK got it within days."
If you want an even shorter wait when 4.2 comes out and 'Check Now' is saying 'no updates' , go into Settings > Applications > All > Google Services Framework and clear it's data. Then check for updates again.
I'm not sure why this works but it does. When I got my 4.2 update, I accidentally tried to install it with CWM installed, naturally it failed and when attempting to get the update again, 'No updates available'. Doing the above got me the update straight away.