Now that they're off the hook for the outcome, it's dribbling out that there were some big power struggles and ideological fights in the State Department over how the United States should approach this, and especially what it should say. Everybody seems to think Obama was on the side of Mubarak leaving in some fashion, but no one will really know until the books are written.
Some commentary emerges. This was basically the stated intent of the Iraq War, to inspire people in the Middle East to take their government into their own hands, that they have the power to topple oppressive autocrats. They got a little messy in a big hurry, and left people across the region with a bad taste for... well, Americans promising freedom. Now, a President's speech in Cairo two years prior, a global economic crash and inflation, the brutal murder of an anti-government blogger, and some Internet "activists" futzing around with the Tunisian government, all together had the totally unintended effect of inspiring the clearest example of a popular uprising in a generation, that toppled and ejected the thirty year police-government of the powerhouse of the Arab world.
If there's one lesson to take away from this nail-bitter event, and who the Hell knows what lessons there are, it's this: Geopolitics is complicated.
EDIT: The military signaled their tacit endorsement of Mubarak's ouster every way they could. When the mob reached the Presidential Palace, the commander of the heavy garrison there actually signaled his men to turn the turrets of the tanks away from the crowd and shut the engines off, to make it clear they weren't going to stand in the way.