That said, testing is moving relatively smoothly on the PTRs, and lots of the content seems like it's pretty well put together. We aren't nearly done with testing yet, though -- we haven't seen most of the Icecrown raid, and we're still waiting on Halls of Reflection, the 5-man where we'll face Arthas. Gear still needs to go into the game and be tuned. There are around 15 different bosses and encounters in Icecrown (that we know of), and if Blizzard continues on the schedule of testing one or two per week, we're looking at six to eight more weeks of testing for just that content. The PTR itself went up just under a month ago, and it seems that we've got at least a month or, likely, more of testing and updating to be done.
All of this information, combined with what we've already learned over the past five years about how Blizzard releases content, leads us to see the patch coming sometime in early to mid-December. It's unlikely we'll see it before the Thanksgiving holiday -- the Pilgrim's Bounty holiday should already be out in the clients, and given the rate at which Blizzard has tested the content so far, it just doesn't seem likely that they'll finish it up in just another month. And anything too close to the holidays might cause problems on Blizzard's staff trying to push out a patch while wanting to spend time with their families.
That said, remember that this is an early bit of speculation -- we may see the patch as soon as Thanksgiving (though don't count on it), or we may not see it until after the new year (which seems like it would be a long time for raiders, many of whom have already conquered even the heroic content). But from what we can tell, seeing the patch hit the live realms on December 8th, 15th, or 22nd seems most likely. Don't hold your breath for those dates, but as a general idea of where it might land, that all seems to make sense.