There is one additional major concern to bring up (and it has been done frequently already in other articles/threads): data security.

Currently, most companies have a strict regulation who has direct access to the data the company's dealing with. The people having direct access to the data (including domain admins) usually are known by name and (hopefully) trustworthy. There are firewalls to protect the data from unauthorized access from the "outside" and usually even within a company. And both for very good reasons.

In "the cloud" the data are some sort of "public". Not only you need to take of the securitiy issues at your cloud host. You also need to pay attention to the way you connect to the cloud.