Glenn Greenwald documents the contradictions in the Establishment's use of the word "terrorism"--which it denied to Joseph Stack, the Austin plane crasher:

Contrast the collective hesitance to call Stack a Terrorist with the extremely dubious circumstances under which that term is reflexively applied to Muslims. If a Muslim attacks a military base preparing to deploy soldiers to a war zone, that person is a Terrorist. If an American Muslim argues that violence against the U.S. (particularly when aimed at military targets) is justified due to American violence aimed at the Muslim world, that person is a Terrorist who deserves assassination. And if the U.S. military invades a Muslim country, Muslims who live in the invaded and occupied country and who fight back against the invading American army -- by attacking nothing but military targets -- are also Terrorists. Indeed, large numbers of detainees at Guantanamo were accused of being Terrorists for nothing more than attacking members of an invading foreign army in their country, including 14-year-old Mohamed Jawad, who spent many years in Guantanamo, accused (almost certainly falsely) of throwing a grenade at two American troops in Afghanistan who were part of an invading force in that country. Obviously, plots targeting civilians for death -- the 9/11 attacks and attempts to blow up civilian aircraft -- are pure terrorism, but a huge portion of the acts committed by Muslims that receive that label are not.

In sum: a Muslim who attacks military targets, including in war zones or even in their own countries that have been invaded by a foreign army, are Terrorists. A non-Muslim who flies an airplane into a government building in pursuit of a political agenda is not, or at least is not a Real Terrorist with a capital T -- not the kind who should be tortured and thrown in a cage with no charges and assassinated with no due process. Nor are Christians who stand outside abortion clinics and murder doctors and clinic workers. Nor are acts undertaken by us or our favored allies designed to kill large numbers of civilians or which will recklessly cause such deaths as a means of terrorizing the population into desired behavioral change -- the Glorious Shock and Awe campaign and the pummeling of Gaza. Except as a means for demonizing Muslims, the word is used so inconsistently and manipulatively that it is impoverished of any discernible meaning.

(BTW GG gives hyperlinks to the claims above; I'm too lazy to copy them all in.)

I have a couple more thoughts on this:

1) The reason I think this was legit, rather than a false flag operation, is that the government isn't immediately calling it terrorism and using it to round up militia groups etc. I think they were caught flat-footed, and so their immediate response was to downplay it until they could figure out how they were going to play it. Fortunately for them, it's fine if they call it terrorism and pass the Building Protection Act of 2010 in a few months (in which all owners of private jets must donate a kidney to the federal government). Nobody will remember the initial reaction and think twice.

2) I was having lunch with someone who pointed out another reason that the government and major media weren't instantly labeling this a terrorist attack: It might cause too much cognitive dissonance among Americans who look like Stack. In other words, it's very convenient to whip people up into a frenzy over brown guys named Mustafa who worship Allah and think the US government is evil. But a white guy named Joe who (it seems) is secular and thinks the IRS is evil...well, people might not reflexively hate that kind of person so much. So the government might not want to taint the wonderful word "terrorist"--which they've built up over the last few years through careful conditioning--by applying it to the latter guy.