Even though we have a set December 7 release date for Cataclysm, we still want to avoid giving out specific dates for upcoming events and patches in the event we need to shift our scheduling around at all to meet production needs.
I'll try my best here to give you useful information without it feeling like a non-answer. :)
Be patient! If you're really hoping to roll brand new characters once the shattering of Azeroth takes place, I'd strongly recommend just waiting. You'll get a sense soon enough for how events will unfold from now until December 7. I suggest you stick to your main characters for now. Very soon the pre-Cataclysm events will begin and they'll continually ramp up in severity and things to do over time, leading up to the shattering (patch 4.0.3a). You're going to want to participate in these events, as they'll only be around for a short time and will not return once Deathwing is unleashed.
[...] One thing we'll be clarifying a bit better next week is the distinction between what is in patch 4.0.3 versus when the shattering takes place.
Patch 4.0.3 will implement virtually all of the content necessary to make the changes to Azeroth, but those changes will actually take place in patch 4.0.3a, which is scheduled to be released shortly after patch 4.0.3.