Build A Map is a new service that allows you to build layers on top of Google Maps. This is different than creating maps in the "My Places" feature of Google Maps. In My Places you can only add placemarks, paths, and shaded shapes. Using Build A Map you can add information from data sets, add shapes, and add custom labels. The service is currently in a private beta so you do have to register your email address and wait for an invitation to try it out. In the meantime you can watch the following video overview of the service.
Applications for Education
Build A Map reminds me a bit of Scribble Maps which also enables the construction of layered Google Maps. While you can do all of the layering features of Build A Map or Scribble Maps in Google Earth, not all teachers and students have access to Google Earth for various reasons. Or if you're in a school like mine that has a 1:1 netbook program Google Earth might not run as well as it should. In those cases Build A Map or Scribble Maps is a great alternative for developing layered maps.
H/T to Google Maps Mania.