The areas and lengths operation only supports measurements in euclidean space right now. These are only useful if the spatial reference of the input geometries are in a projection that minimizes distortion for the area of interest. You can project the input geometry to a custom hotine or equidistant azimuthal projection to minimize distortion, then call the operation to get areas and lengths. I've attached an example that builds on the sample in the SDK. In 10.1 a couple of additional calculation options will be added to the areas and lengths operation to optimize results. The measure action in the API supports client-side geodesic calculations when input geometry is in Web Mercator or DD, otherwise it assumes euclidean space.