Mark’s cold shower is entirely correct. But I think he may be insufficiently pessimistic. The pieces haven’t been all thrown up in the air to fall back randomly; the system has a lot of structure and the dice are heavily loaded in favor of the army, which is the only institution to come out of the recent upheaval intact, even stronger having shed its Mubarak and Suleiman front men and more important, having shown that it can do the same with the next set.
Before Mubarak was thrown under the bus, Robert Springborg published this very sobering reflection, and this afternoon Professor Sunshine was on NPR describing the pervasive dominance of the Egyptian economy by the military.  Before we get all grateful to this enterprise for sparing us a Levantine Tienanmen Square or Mexico City ’68, it’s worth reflecting that it is more like the Chinese PLA than a normal country’s military.
The top levels of the Egyptian army (and other forces, presumably) have been pruned of democrats and troublemakers for three decades, and the guys who remain are bought and paid for with a flood of loot. Mubarak and Suleiman are, it seems, more properly regarded as the generals’ (cashiered) agents than the other way around. The soldiers are just conscripted citizens, and may or may not follow orders to enforce oppressive policies, but the idea that the brass is going to go along with a constitution (in practice or on paper) that threatens their beach houses, Swiss bank accounts, and townhouses in London and New York bears a lot of scrutiny. Mubarak didn’t accumulate a fortune in the billions without letting generals, and probably colonels, get in the habit of wetting their beaks.
The Interior Ministry troops/thugs/cops and their officers are a wild card that’s received little attention since the camel and horse performance. But they haven’t gone away. And it’s they and the army that have the guns and pliers and oubliettes, and a long habit of being comfortable using them. It is more than a little likely that the latest military coupsters in that unhappy country will be able to get back to business as usual, and that Mubarak’s last bitter legacy will be his successful suppression of political institutions and organizations that could have stood up to them. This story is so not over yet.