Cloud services can shut down due to financial problems. Some respectable cloud services have shut down after a severe hacking incident. Companies can and do lose data that they thought was safe.
The important thing to realize is that cloud services carry the same risks as other IT options, they are just transferred to a third party. A provider could fail. So if you are looking for cloud services, be sure to:
1) Choose a Cloud Service Provider Carefully
What kind of data will the provider be storing for you? The more critical your data is, the more important it is to choose an established, financially stable company. For example, Salesforce.com is going to have more safeguards in place than a small CRM provider, even though neither is bullet proof.