I don't know about you, but this sentence on the Review Order screen has always seemed wrong to me:
Your order is not complete.
Every time I see it I get the feeling that there is a problem with my order, that I've done something wrong.
I'd like to suggest that the sentence be changed to "Your order has not been submitted yet" or some phrase that's a little less...well, I don't even know the word to use. Or even remove the sentence altogether, since the next sentence tells the user that the order needs to be submitted.

Maybe simply adding a "yet" into the existing sentence would help? "Your order is not yet complete." I dunno... I'll think about it, but it'll never be perfect. You can change it in the checkout messages settings, though.