One of the challenges customers always have is, how to select the right cloud partner and fairly often security drives this selection. The Cloud Security Alliance published the Cloud Controls Matrix quite a while ago and in addition a Consensus Assessments Initiative Questionnaire and a lot of request for information/proposal are based on this material.
Therefore we made our answers to these questions publically available: Cloud Security in Office365. In the meantime the Cloud Security Alliance worked on a Security, Trust and Assurance Registry (called STAR) with the goal to have all these answers in one place. Kellie Ann Chainier (she works at Microsoft on a lot of these challenges) just published a corresponding blog post: Cloud Security Alliance makes cloud security more transparent with new STAR Registry – short and worth reading