The "You can't secure the cloud" article published by Hoff on Rational Survivability discusses whether you can make the cloud solutions as secure as enterprise (walled garden) ones. Here's a great summary:
Yes, it’s true. It’s absolutely possible to engineer solutions across most cloud services today that meet or exceed the security provided within the walled gardens of your enterprise today.
The realities of that statement come crashing down, however, when people confuse possibility with the capability to execute whilst not disrupting the business and not requiring wholesale re-architecture of applications, security, privacy, operations, compliance, economics, organization, culture and governance.
The rest of the article is also well worth reading.