I'm about a quarter of the way through the book now and loving it but I'm interested in how historians view it. Any qualms or praises for it? Things I should be wary of as I continue?
The FAQs section has a whole slew of answers for questions concerning "A People's History ..."
http://www.reddit.com/r/AskHistorians/comments/2wc99z/why_did_america_enter_wwi/
Scroll through this thread and you'll see something of the issues numerous historians have taken with Zinn's portrayal of events.