There was little indication when the calendar year began that 2011 would be a year in which multiple North African and Middle East tyrants would face genuine threats to their job security (and I hope you see the dripping sarcasm in the selection of those final two words).
Beginning with Tunisia, continuing to Egypt, to Libya, to Bahrain, and to Syria, the internal and external pressures on various tyrants have sustained itself. The people of Tunisia and Egypt already are rid of their dictator, though what will replace the government structure in either land is still to be determined.
The demise of Libya's leader seems imminent, as rebels aided by NATO have taken control of that country's big cities and are rapidly advancing toward taking over Tripoli, the capital city.
For now, change of leadership isn't guaranteed in Syria, though various Western leaders called upon that nation's president to give up his power. That's not going to happen without some kind of fight, but for now those governments don't appear committed to sending troops to bring about change.
One leader -- of a movement, not of a nation -- also met his demise; the death of Osama bin Laden will not end al Qaeda, which has morphed into smaller cells, but his death provided a symbolic smashing of the organization.
Will other leaders be replaced (or worse) before the year ends? There's no way to know, but perhaps the larger issue is whether the momentum that began in Tunisia can continue. Right now, the answer appears to be yes.