There are now 100 million active users — users who log in at least once a month — with half of those users signing in at least once a day. Fifty-five percent of them access Twitter via mobile; 40% actually don’t Tweet but simply dip into their Timelines to keep tabs on what people are saying.

The site’s users are breaking records too. During the World Cup last year, the number of Tweets peaked at 3,300 per second; that number jumped to around 8,900 per second two weekends ago when Beyonce Knowles announced her pregnancy live on MTV’s Video Music Awards.

Part of that is due to a growing userbase, but Costolo also says the company has been focusing on shifting over to a new infrastructure that could properly scale and keep up with that growth. (For a complete chronicle of Twitter’s growing pains, click here.) He admitted the notorious “Fail Whale” screen that pops up when ever servers crash may be the most popular of its kind in Internet history for all the wrong reasons.

On the subject of Promoted Tweets, or sponsored Tweets, users currently only come across ones from brands they’ve decided to follow. That will change moving forward. Users will eventually see Promoted Tweets in their Timeslines from brands they don’t follow based on what he calls user activity, including who and what they do follow. To that end, the company will roll out a self-service feature companies can use to generate their own Promoted Tweets.

What about Twitter’s newest competitor, Google+? “No doubt they’ll get massive users,” Costolo, a former Google employee, said of the company’s latest social effort. “They’re bundling it with the Android platform. You can’t not see that red number [update] on the upper right hand side. That’s going to draw an incredible amount of usage. But how we see ourselves differently, is how can we simplify the UI and what we can edit out. I think these platforms will add [features], but we’ll try to edit ours down.”