The project is a collaboration between MIT and the Lawrence Berkeley National Laboratory and appears to be slightly experimental at this stage, at least when you look at the signup disclaimer:
I understand that the data in this database is computed, and may not be accurate enough for my application. I agree not to hold the developers, contributors, and hosts of the Materials Project liable for any accuracies in the data, or consequences thereof. I agree not to use automated scripts to collect large fractions of the database and disseminate them. If you are interested in large datasets, please contact the developers.
Via MaterialsProject