Poll
You make a valid point that the subscriber base that was polled is not a perfect cross-section of the military, and probably doesn't include a lot of Iraq-posted personnel.
But I'm not getting all my information from polls like this by any means. I read what people who are on the front lines are writing--their opinions, their analyses, and how they feel about things. It isn't all gung-ho positive, but most of them think they are doing something important.
And again, the one thing they all seem to have in common is astonishment and anger over how the war is presented by the media back home.