It's been a while since I read it but I agree with aj it was rather leftist.
To me, facts are facts, whether its left or right. I try to see things as how well they are presented and what evidence is put forth. Cant argue with evidence just because you don't agree with a left stance.
I am not saying Zinn's book is 100% factual, but I think its more important to view a position based on the evidence, as opposed to whether it has left or right leanings. Who cares. As long as its correct.
For what its worth, if I had to classify myself as anything, Id be an Independent.