A short report by the New America Foundation, the full title being 'The State of Global Jihad Online; A Qualitative, Quantitative, and Cross-Lingual Analysis':http://www.newamerica.net/sites/newa...Online_NAF.pdf

It starts with:
It is only a matter of time before terrorists begin routinely using Twitter, Instagram, and other services in ongoing operations. We have already seen this in a limited manner from al-Shabaab, which tweets its #JihadDispatches on recent battles. But those delivery mechanisms are unlikely to replace the forums as the main environment for conversation and information distribution among jihadis. Twitter and the like provide a more public platform than a password-protected forum, but one critical utility of forums for jihadis is the ability to have relatively private conversations.
The paper looks interesting, but this is not my field. One headlined point does resonate with me:
Imagine how much more of a spectacle it
would have been if the Mumbai attacks and hostage-takings had been live-tweeted alongside instantly uploaded pictures and video of the events.