October was a good month for Twitter. All those election Tweets brought a 25 percent increase in U.S. visitors from the month before, to 1.45 million unique visitors, according to comScore. (Worldwide, the number was 5.6 million in September). Since January, Twitter has experienced a 16-fold growth in the U.S. And that is just visitors to Twitter.com. These numbers don’t count all the people who send and read Tweets from other Websites, desktop apps, or their mobile phones.

Twitter is having its hockey stick moment in terms of its growth just shooting up. Last week it may have delivered its billionth Tweet, at least nominally. And it looks like it is approaching escape velocity. If it doesn’t break up from all the pressure and is able to keep its service up and running more or less, it could soon—gasp!—break into the mainstream.

That little red line at the bottom of the chart, just for reference, is FriendFeed. It is still scraping the ice in terms of growth. Comscore only measures 150,000 unique U.S. visitors in October (550,000 worldwide in September). But that’s just below where Twitter was last January. And FriendFeed is a lot younger than Twitter, having launched publicly only last February, compared to July, 2006 for Twitter. Maybe a year from now it will be hitting its hockey stick.