Twitter has released its second transparency report

The list disclosed data requests from over 30 nations, and revealed that the US government was responsible for 815 of the 1,009 information requests in the second half of 2012 – just over 80 percent of all inquiries.
Twenty percent of all US requests were ‘under seal,’ meaning that users were not notified that their information was accessed.
The overall number of requests worldwide also steadily increased last year, rising from 849 in the January to June 2012 period to 1009 in the July to December 2012 period.
Twitter’s legal policy manager Jeremy Kessel blogged that, “it is vital for us (and other Internet services) to be transparent about government requests for user information.”
“These growing inquiries can have a serious chilling effect on free expression – and real privacy implications,” he wrote.

 http://leaksource.wordpress.com/2013/01/29/twitter-reveals-us-government-makes-80-of-info-requests/