Cloud Computing Office Suite

It’s been said that such a service is both good and bad in several discussions.

So, what are the reasons for and against it?

Here are the starting off points:

Drawbacks / Concerns:
Loss of control of business logic
Possible [ probable? ( Google Docs ) ] exposure online of confidential data.
Loss of control over accessibility, you can do nothing if the service goes down.

more?

Benefits:
Disaster recovery, you have off site storage of critical data with real time backup, so a disaster striking the office doesn’t cost you any data loss.
Accessibility, everyone in the office has full access to their work tools, anywhere.

more?

What would such a service have to have to make it a viable option?