Edge probed Sony UK boss Fergal Gara on the PS4 launch, trying their best to get some hard numbers out of him. He wouldn't give on that (they're still working that out), but he had plenty to say about the launch window.
He's speaking for the UK territory specifically, saying that there is going to be "ample stock" for the first two to three months -- the launch window. He goes on to say that "anyone that has preordered a PS4 now is almost certain to get it before Christmas," and that there will be more beyond that.
All of that said, Gara doesn't feel that customers will be able to walk into a store on launch day and get a PS4. He advises getting on a preorder list to get in good.
As you'd guess, they're prioritizing based on number of preorders, with North America and Europe being the two focused regions for launch.
Do you have your preorder in?