This is really mostly MSM/blogosphere hype. These revolutions started when people set themselves afire, and risked their lives confronting the army/police. FB might have helped (Youtube probably even more, Twitter almost trivial) but in the same way that a cellphone would.
Governments are now using social media to track dissidents as well, so it's not at all clear the net effect it positive.
Agree with your second point. But Twitter helped spread the YouTube videos so I doubt Twitter is trivial. Communication, whether it's the Internet or cell-phone, helped the revolutions by connecting people and organizing them. But yes, we don't know the net effect and I think it's impossible to know.
Governments are now using social media to track dissidents as well, so it's not at all clear the net effect it positive.