An interesting article / research study that used Google Earth imagery to find sites that were used for food production within the city.
To read the article: http://www.npr.org/blogs/thesalt/2013/01/08/168895084/finding-chicago-s-hidden-farms
From the Google Earth Newsletter:
Follow Your World
We're often asked about the age of satellite imagery and when new content will be updated. While we aren't able to tell you in advance when our imagery will be updated, we can now notify you after new images are added to an area that you're interested in. With the newFollow Your World website, you can register points on the globe, and we'll send you an email whenever imagery is updated there. Learn how to submit your imagery requests here!