One of the most valuable aspects of the Library of Congress' National Digital Stewardship Alliance (NDSA) is that it provides a forum for sharing expertise and experience among institutions trying to preserve the nation's digital heritage. The latest example is the Report on Digital Preservation and Cloud Services (PDF) written by Instrumental for, and published by, the Minnesota Historical Society. This is an excellent overview of the strategic and technical issues surrounding the potential use of a wide range of cloud services for preservation. I strongly recommend reading it.
Also, Rebecca Pool has a short piece on the same topic here, based in part on an interview she did with me some months ago.