One of Twitter's primary concerns is that the number of active users -- those who use the network at least once a month -- continues to grow at a healthy pace, and its latest quarterly earnings confirm that the social network has been eating its vegetables. After reporting a solid growth of 14 million active users last quarter, the service brought in 16 million this time around, reaching a grand total of 271 million. This is an increase of 6.3 percent, which is an improvement over last quarter's 5.8 percent (though not quite as good as the ten percent growth the company saw a year ago). Not bad, given that it had to admit a slowing number of new users earlier this year in its first earnings report as an IPO. Of this number, Twitter acknowledged that 78 percent of them are actively using the service on mobile devices (this is reflected in the fact that 81 percent of advertising revenue comes from smartphones and tablets).