In the interest of ensuring "...as little worry, panic, confusion, mass hysteria, riots in the streets, armaggeddons, etc... as possible," Atlus is getting the word out officially that the North American servers will not be running until Tuesday, October 6.
This shouldn't cause many problems, unless of course you manage to score a copy early. If this is the case, you can still play the single player game, but connecting to the servers will result in a PSN error. You'll still have access to in-game content, but lose the ability to see how other players died, get clues and play co-op boss runs.
Demon's Souls ships October 6, the same day the servers turn on.