Joe suggested that I compare what's going on in Egypt to what happened in Poland in 1980-81, when I was at the embassy there. That was when Solidarity was set up and, after several months of uncertainty and rising revolt against the Communist regime, martial law was declared. (Devotees of this blog - both of them - will remember that I made a similar comparison during the Iranian protests in 2009).
First, an obvious similarity: the regime is old, worn out, and people are disgusted with it and with their parlous economic situation. But remember: Solidarity was born in the summer of 1980; martial law was declared in March 1981, but the communist government lasted until the end of that decade. So Poles endured a long, painful time of repression after a peaceful, mass movement against the communist regime.
Second, a potential similarity to ponder: the Polish army was not about to attack Polish civilian demonstrators. When martial law was declared, the authorities relied instead on a special paramilitary force drawn from the scum of society and trained in secret for several months. So now the Egyptian police have evaporated and the army looks like it doesn't want to attack civilians...so is there someone else out there? Maybe not, since this has all happened so quickly.
Third, a big difference: there was no force like the Muslim Brotherhood - a well-established group with lots of overseas links and, presumably, access to money and other resources. Solidarity was only created in 1980 and, despite any accusations you may have heard to the contrary, was not/not supported by the U.S. government or any other outsiders. While it was weak, it didn't have compete with another popular but very undemocratic and illiberal group.
Fourth, another big difference: Poland was one of several Warsaw Pact members who had sought to escape Soviet domination. Perhaps there was a shared anti-communist ideology, but nothing that compares to the aggressive Islamism that has spread in the Mideast and North Africa ever since the Iranian revolution in 1979. Poland was actually a leader: the Solidarity movement was the first ever mass movement of workers against a communist workers' paradise.
In sum, I don't see too many points of similarity between Poland then and Egypt now. Unfortunately.