I think it can and has. Look at what social media did to help fuel the arab spring and occupy wall street. Whether those have long lasting effects and whether you consider those effects "significant" is subjective to an extent. Also, look at the modern American political process. So much of that is driven by social media and it certainly has an impact on the outcomes. Also, the amount of good it does on an individual level is pretty amazing too. Reddit has been a great example of this imo. I recall donating money to help a little boy's parents pay for his surgery at Duke Medical Center. I wouldn't have known about it without reddit. Ask that kid and his family if social media can effect positive change. Social media cannot fix a broken idea or organization though, which is what we saw with Kony and to an extent OWS. Eventually, a really big and well run movement will harness social media to it's fullest potential and we will likely see something of unparalleled change. Hopefully, it's a positive "thing".