During today's Facebook earnings call, head honcho Mark Zuckerberg told investors that overall people spend "more mobile time on Instagram than Twitter", pointing to comScore numbers to back up the claim. Not a bad justification for that huge investment.
That number shouldn't be as shocking as it sounds. But think about how much more engaging staring at and taking all of those pretty pictures on your phone is compared to banging out 140 characters and reading other people's tweets. Plus, Instagram is a mobile-based service, and Zuckerberg's numbers don't take into account the way people use Twitter on their desktops