I enjoyed it a lot. I had overlooked it in theaters, but a friend forced me to sit and observe. The magically sterile part I think is another thing the viewer speculates on eternally. Religious views, apocolyptic thoughts, the environment.. what triggered it, the supernatual, mankind himself, the environment, disease, milk, sunshine.. It was another fun thing to debate about.
I don't think the one baby saves humanity.. I'm sure that girl was pumped with more sperm then a whale afterwards.. but the fact it's there means that mayhap the people whom thought it was the end of the world have hope of otherwise.
I really thought it was interesting that they sold suicide kits. That was just insane to me.. to be so open about it, and just publically let people know that "Yup, there's pretty much no reason to live anymore." I wouldn't like to think of America as a whole so pessimistic.. that might be a bit too scary for this little chica..