Knowing that the bulb at the bottom isn't just for show, it looks like we're about 2/5 of the way there. Unless Black Ops steals away a ton of players, I'd expect the pace to continue at a similar rate (less people playing frequently, but a small number more actively completing challenges) that it has over the first five weeks of the game's availability... I'd guess mid-to-late December or so.
Just a guess, though. I also haven't reached the cap and probably won't anytime soon since I don't have much time to play right now, so I'm not extremely invested or anything.