Nokia has stated that the official release date will be sometime in early 2013. I would anticipate that the start of the update roll-out shouldn't be too far away, and be finished by the end of March.
what is the reason that Nokia or Microsoft can't/won't provide a firm date? Is it because there are variables that are not controlled by either, such as carrier tests, therefore you can't give an actual date? It doesn't bother me even though I'd like an actual date as well. I've accepted that neither Nokia or Microsoft will provide one, but I'd just like to know the reason why. I'm lead to believe that this is more to do with Microsoft than Nokia.