Twitter's 100,000,000 users

"He said active users, who log on at least once a month, rose 82% this year.

Half of these 100 million log on at least once a day.

Twitter raised $400m (£250m) in venture capital funding this summer."

BBC News - Twitter says it has 100 million active users

The 100 million users, half of which use it on a daily basis combined with the ease of use on mobile phones and smart phones, provides an amazing sample population for social activity.

Our work at the Web 3.0 lab uses geo-tagged twitter data. We try to use twitter densities in space to determine events on the ground. We have used twitter to track Chicago Cub games and Dolly Parton concerts in London to protest in Madrid, Cairo and Bahrain to finding a good place to eat in Istanbul or Amsterdam.

The more people using twitter, the more people with smartphones and the more people willing to post geo-located data means a larger public supply of real time time is emerging for everyone to use.

Privacy issues are a major concern, but we use public information all the time. Fashion is a very key form of public information exchange. You can tell so much about a community from what people are wearing.