Sven E. Hug and Martin P. Braendle have self-archived "The Coverage of Microsoft Academic: Analyzing the Publication Output of a University."
Here's an excerpt:
This is the first in-depth study on the coverage of Microsoft Academic (MA). The coverage of a verified publication list of a university was analyzed on the level of individual publications in MA, Scopus, and Web of Science (WoS). Citation counts were analyzed and issues related to data retrieval and data quality were examined. . . . MA surpasses Scopus and WoS clearly with respect to book-related document types and conference items but falls slightly behind Scopus with regard to journal articles. MA shows the same biases as Scopus and WoS with regard to the coverage of the social sciences and humanities, non-English publications, and open-access publications. Rank correlations of citation counts are high between MA and the benchmark databases. . . .Given the fast and ongoing development of MA, we conclude that MA is on the verge of becoming a bibliometric superpower. However, comprehensive studies on the quality of MA data are still lacking.