My mother was born and lived her entire life in New Jersey, and my roommate was from Missouri. I grew up in New Jersey, but have lived all around the country.
I don't know, my mother's parents just always pronounced it ZO, and that's just the way her name was pronounced. As a result, when I first heard ZO-EE, I thought THAT was strange.
I'm beginning to find it interesting that my mom had the name Zoe, because she was born in 1928, when it was a very very unusual name. I know she was given it because it was my grandmother's middle name, and she was born in 1906, when the name Zoe in the U.S. was just about unheard of. I wonder how it got started in my family, who first thought of using such an unusual (for the time) name, because I believe that I heard that it was my grandmother's paternal grandmother's name.
I didn't realize until reading the comments page for Zoe how uncommon it is to pronounce it ZO. I had always thought it was a legitimate alternative pronunciation.