Both cloud computing (specifically SaaS) and SOA promote the idea of services for transforming software to a commodity.
However, most SaaS providers focus mainly on providing the service to the end user, but the products aren't well suited for back-end integration.
Most providers provide only an API access to their service.
Some provide also integration with other specific SaaS services
But if one wants to aggregate data and functionality from different services which weren't planned to work together, he needs to use traditional tools to access and consolidate them - loosing many of the benefits of SaaS
A concrete example Consider an organization that uses a SaaS solution for CRM, and another one for HR management. both of them will probably include an API (REST or WS) that allow to interact with them. However, most chances, that they won't allow you to directly synchronize user profiles between them. To do so you need to pull data from the HR system, and send it to the CRM system. this mechanism isn't currently available as a cloud service. and you will need to use "standard" integration technologies - either dedicated tools (ESB, EAI) or custom code, that will run on a server that you need to maintain.
What do you think will be enablers of cloud based integration ("Cloud Service Bus")
Development of common Web Services API's for SaaS providers (like all e-mail providers support SMTP and POP3, there will be a common CRM protocol and HR protocol)
Development of cloud based broker services with capabilities such as message queuing, transformation engines, workflow engines, etc.