Political revolutions are often closely linked to communication tools. The American Revolution wasn’t caused by the proliferation of pamphlets, written to whip colonists into a frenzy against the British. But it sure helped. Social networking, a distinctly 21st-century phenomenon, has already been credited with aiding protests from the Republic of Georgia to Egypt to Iceland. And Twitter, the newest social-networking tool, has been identified with two mass protests in a matter of months — in Moldova in April and in Iran last week, when hundreds of thousands of people took to the streets to oppose the official results of the...