There is an alternative way to access MBooks other than through UM's online catalog Mirlyn. You can harvest the MBooks records directly via our OAI interface. The University of Chicago has done just that, and integrated these records into their library catalog.
Excluding serials, as they were more problematic to integrate, they provided access for users to MBooks and Google Books links from the catalog, for books they held.
As an example, go to http://lens.lib.uchicago.edu/ and search for "An historical sketch of the native states of India in subsidiary alliance with the British government". The second record provides the link to the MBooks full text of that book.
We're very interested in hearing from other libraries that are using MBooks records in their online catalogs.
Only records for MBooks available in the public domain are exposed through OAI. We have split these into sets containing public domain items according to U.S. copyright law, and public domain items worldwide. There are currently over 121,000 records available for harvesting. We anticipate having 1 million records available when the entire UM collection has been digitized by Google. For more information, see http://www.lib.umich.edu/mdp/info/OAI.html.