The microblogging service has a total of 200 million registered users, but how many of those are actually regulars has been open to debate. Costolo, in an informal chat with tech reporters, revealed that exactly half of them log in monthly -- a number he says is up 80% since the beginning of the year.

The CEO offered a whole raft of statistics to prove that Twitter is healthy and growing like a weed -- especially on mobile platforms. Some 55 million users log on to Twitter from their phone or tablet every month. Web-based users are on the rise, too: Twitter.com now sees 400 million visitors a month, up from 250 million at the beginning of the year, Costolo says. Less than 40% of users don't tweet at all, according to the CEO, preferring to simply follow the timelines of others. That figure stood at 70% at the end of the year. "We're excited about that number," Costolo says. "That's super healthy."