The short answer is that when you put your data on the cloud the provider has the technical capability to do what they want with it. They could sell it, trade it, share it, etc. What is keeping them from doing just that is a) the terms of service or contract agreed (read it to make sure they don't have rights to your data as some claim rights over anything you upload), b) law - although in most places the law is ambiguous and/or missing on this point, and c) public opinion, see instagram's recent fail on this issue.
In most cloud services agreements (at least consumer ones) there is a clause saying that the provider can change the terms of service at any time, so they could theoretically decide to claim ownership to all data and then sell it to the highest bidder. Few companies will go down that route as it guarantees that nobody will ever use their services again, however if a company went out of business it's possible that method could be used by the administrator to make the most out of the failed company's assets.
So do you have any semblance of control of your data in the cloud? Absolutely not, unless you control something about the data. If you encrypt the data at source using an independent utility and then store the encrypted files on the internet you can prevent its misuse, otherwise you just have to accept the trade-off of flexibility versus control.