Always happy to see a dictator get the heave-ho, although events have proved that Mubarak's regime was not dictatorial enough. Ya gotta be a socialist to do dictatorship right. Look at the Castros in Cuba - fifty-two years and counting.
Still, I'm with Edmund Burke on revolutions: "The effect of liberty to individuals is that they may do what they please: we ought to see what it will please them to do, before we risk congratulations". If there were any prior history of democracy in Egypt, any institutions other than the armed forces to provide continuity, one might be more sanguine. It is always possible that some kind of new, civilian-run order will emerge from the inchoate protests that brought Mubarak down - but it's not the way to bet.
In general, a prolonged period of submission to arbitrary power reduces the possibility that it will be replaced by responsible self-government when overthrown. The exceptions that test the rule are the more western members of the old Soviet Bloc, who made the transition remarkably well. The clue there lies in "more western" - they were only subject to despotism for forty-five years, and retained the memory and the habits of responsible self-government developed before Soviet occupation.
As far as the Middle East is concerned, the most optimistic precedent is the way Ataturk and the army broke with the supranational Ottoman inheritance to impose a new, nationalist order on Turkey. Unfortunately that option is not open to the Egyptian military. First of all, Egyptian nationalism produced the pan-Arabist Nasser, not a westernizing Ataturk. Secondly, the Muslim Brotherhood is not tainted by association with obscurantist clericalism and is the only organized opposition.
I think the military will have to do a deal with the Brotherhood. Let's see what the terms of that deal are before celebrating a brave new dawn in Egypt.