Since Microsoft announced today that they will have 2-3 million Xbox360's ready for November I see no reason why I shouldn't take the $50 deposit I have and buy a PSP (Mercury or Ridge Racer) or GameCube (WWE DoR2) game with it. So I decided to cancel it sometime soon and buy a new game 'CAUSE I REALLY NEED ONE (speccially for PSP).
I seriously doubt that the 360 will sell more than 500 thousand units on launch date. So there will be more than enough units left (about 2 million left maybe?) for those that didn't pre-purchase.
Now for PS3 it should be a different story. I remember the PS2's launch it was hard to find if you didn't preorder. Luckly I had my PS2 preordered. Now for PS3 I expect shortages; but I don't think I'll buy a PS3 before the FFVII remake comes out so it should be a few years after launch before I buy one.