Twitter has announced some new stats on usage of its service. In the first quarter of this year, the number of tweets per day increased by 41%, while the number of monthly Twitter account signups grew by 52%. In the same time period, there was a 50% increase in ‘monthly unique mobile signups’. Twitter digs into those stats a bit more, saying that in Q1, the number of users of the official Twitter app for Android grew by 104%, versus 72% for iPad, 55% for iPhone and 55% for BlackBerry. One last big stat though: Twitter is now recording 155 million tweets a day on the overall service – up from 55 million this time last year.