Time has an illuminating interview with "Abu Qaqa al-Tamimi," an Iraqi insurgent trainer, that among other things sheds light on why so many suicide bombers in the country have been foreign fighters rather than Iraqis:

Most of the more than 30 bombers he says have passed through his hands were foreigners, or "Arabs," to use al-Tamimi's blanket term for all non-Iraqi mujahedin. Although he says more and more Iraqis are volunteering for suicide operations, insurgent groups prefer to use the foreigners. "Iraqis are fighting for their country's future, so they have something to live for," he explains. He says foreign fighters "come a long way from their countries, spending a lot of money and with high hopes. They don't want to gradually earn their entry to paradise by participating in operations against the Americans. They want martyrdom immediately." That's a valued quality sought by a handler like al-Tamimi, says counterterrorism expert Hoffman: "It's one less thing for the handler to worry about--whether the guy is going to change his mind and bolt.

Makes sense. Meanwhile, al-Tamimi—a pseudonym, obviously—claims that he was radicalized after being tortured in Abu Ghraib by occupation forces; which could be true or not, though he does seem to have used prison time productively to become more religious and develop further terrorist contacts. (He was originally a member of Saddam's Republican Guard, although as with most Baathists joined up with radical Islamic networks in 2004.) Another point: as Doug Farah has noted, one would think that capturing people like al-Tamimi would probably be much more effective for purposes of counterinsurgency than worrying about all those "high-ranking lieutenants," since the trainers and former military men seem to have all the semi-irreplaceable skills. But then, the Republican Guard alone numbered some 175,000 before the war, and that doesn't include Mukhabarat (100,000) and Fedayeen Saddam (~40,000), so it's not like people like al-Tamimi are at all in short supply...

(Those numbers, by the way, come from John Robb, who has argued, persuasively I think, that the United States is fighting a much bigger insurgency than we've been lead to believe.)