Twitter just keeps on growing. CEO Dick Costolo took the stage at The Economist's Ideas Economy: Information 2012 event today and offered a bit of information about how Twitter is doing behind the scenes. Yes, the company just "took flight" with a slightly-modified logo, but arguably bigger news is that the service now handles over 400 million tweets per day. The last number we heard for total daily tweets was 340 million, which analytic company Dataminr revealed back in April, and Twitter said back in October that it had 250 million tweets per day. Other than the increase in volume, Twitter is also seeing increased revenues thanks to its still-recent push for advertising on its mobile apps and website. Forbes quotes Costolo as saying that "mobile revenue is already doing delightfully well," and that mobile surpassed the company's non-mobile revenues for the first time a couple of weeks ago. It's an impressive achievement, considering that Twitter only began to offer advertiser-promoted tweets in the mobile timeline back in March. According to Costolo, its mobile users "are more active and log in... more frequently," which may account for the revenue bump.