Here's what happens when a dictator has access to an off-switch for an entire country's Internet: Via the Committee to Protect Journalists, a visual representation of Egypt's Internet traffic on January 27th.
The swell is almost as interesting as the dropoff. Traffic looks to have roughly tripled in the space of just a few hours before it was cut down to nothing. The graph's creator, Craig Labovitz, the chief scientist of Arbor Networks, explains that this is a "graph of Egyptian Internet traffic across a large number of geographically and topologically diverse providers on January 27th."
Update: The original graph contained a typo and only a single day's worth of data. The folks at Arbor Networks sent along an updated version: