One is that we have thrown dry timber into the Islamic fire.  This is true.  The infidel is back on the crusade in the holy lands, and the radicals have responded. 

The other, is that Al Qa'ida has largely been defeated in Iraq by fighting a two front war: Through the military might of the United States and through the resentment and resistance of the Iraqi militias who tired of their indiscriminate killing.  This is also true.

What does this mean?  Al Qa'ida is weaker at the moment because they have been drained of resources, hardline fighters, and the loss of several top combat level commanders.  Are they gone?  Not at all.  But their current ability to carry out transnational acts of terror has been significantly degraded.  It also means that we are dealing with a homegrown insurgency in Iraq that is just as capable of inflicting damage on U.S. forces as Al Qa'ida, albeit that the probability of these factions carrying out attacks on the United States proper is low.  The real problem will be similar to the aftermath of the Soviet occupation of Afghanistan.  There will be scores of radicalized fighters who will no longer be gainfully employed in the jihad against the U.S. occupation of Iraq, and probably seek to join the jihad elsewhere with other groups; the Shiites siding with Iran and Hezbollah, the Sunnis possibly with Al Qa'ida against the United States, or with Fatah al-Islam in Lebanon to fight against the Israelis (depending on whom they hate the most). 

You could also think of it in this manner: they had plenty of hate before the Iraq war, and carried out numerous attacks on the United States and its international interests (and other countries as well).  So obviously the Iraq war wasn't the birth of terrorism, nor will it be the death knell for it.  I would assess that it will remain the status quo, excepting the fact that they have U.S. troops to fight against right now rather than civilian targets at the present time.

So yes, the GWOT has played a large hand in the lack of attacks on the United States, but it won't be the end of it.  If you want to end it, you have to kill them all.  And that is not going to happen.  That would be like ridding the world of cockroaches.  So, in the end, it is what it is: we are fighting and killing terrorists over there, but they will be back one day.  Doing nothing didn't work out for us either.  Bombed if you do, bombed if you don't.