Cloud services are hosted by all kinds of people and organizations nowadays. Some organizations offer very highly available systems that could withstand the failure of an entire part of the country while others are offered out of a person's basement (really... an old boss of mine hosted a "cloud" service out of his basement). Some providers even cater to niche markets like the eco-friendly market by offering green cloud services, green virtual private server hosting, and green web hosting. Although good for marketing, niche factors don't determine what a "good" cloud provider really offers.
Utilizing cloud services is a form of outsourcing, so the primary business drivers are reducing total cost of ownership and not negatively impacting the quality of the IT service delivered. For the most part, organizations are most successful with outsourcing business support processes while keeping the IT infrastructure and applications for core business services maintained internally.
When evaluating competing cloud services, it is important to look at what the hosting organization provides in terms of the service offered and the availability/performance guarantee. If the hosting company stores your organization's data in a single datacenter at a single site, then this creates a risk of loss in the event of a catastrophic failure or natural disaster at the service provider's datacenter. Perhaps the provider has multiple sites, but relies on tape backup and restore in the event of a failure at the primary site.
Other factors around availability, performance, and overall service quality need to be considered before signing a contract with a cloud provider. When you trust your data to a cloud provider, you are only as highly available as they are. Furthermore, in the event of a disaster affecting a service provider, their internal DR plan will probably be to restore the biggest and highest paying company's data first, so smaller organizations could be at a bigger disadvantage.
The business case for cloud services exists because an organization can manage their IT costs as operational expenses rather than capital expenses and the total cost of ownership (TCO) goes down in some instances (though not as often as you might think). Unfortunately, the use of some cloud technologies can cause an organization's IT service to be less highly available than if it were offered internally by the organization's IT staff.
High Availability, Business Continuity Planning, and Disaster Recovery