Twitter has come long way since its start today in 2006. Six year old twitter sees 340 million tweets every day, an average of 1 billion tweets every 3 days. An amazing feat for a little bird with 140 million users.
By the way Twitter recently included 5 more cities to its local trends. These are Ahmedabad, Chennai, Hyderabad, Bangalore and Delhi. Mumbai is already part of Twitter local trends.
Those cities which generate a sizable number of tweets worldwide are included in local trends.