@Gargron Wouldn't surprise me to see another 1-2M users join before the end of the year.

But, another number that is not getting as much attention: the number of posts per month. This has jumped from 471M in Sept. to 496M today, and likely to reach 500M by month's end,

Which, to me at least, is a strong indicator that people aren't just creating accounts, they are sticking around.