Where are the limitations and the opportunities for businesses looking to embrace the cloud for collaboration functionality? Industry analysts have been consistent in their guidance to enterprises here — look before you leap. Know what you gain and what trade-offs you might have to make — irrespective of whether your decision is to stick with on-premise, migrate completely to the cloud or adopt a hybrid model. In 2009, pragmatism will be the order of the day as enterprises strip away the hype, roll up their sleeves and get into the nitty-gritty of service-level agreements and uptime guarantees, data retention and privacy practices, support and maintenance, and customization options in order to make informed decisions about where the cloud represents the best option and where on-premise software fits the bill.
http://gigaom.com/2009/02/21/the-enterprise-the-cloud-and-5-key-drivers-for-2009/
The emerging consensus is to begin with the "hybrid model", as mentioned above. Migration completely to the Cloud seems premature, while sticking with only on-premises infrastructure ignores the benefits of Cloud computing.
But, as also mentioned above, questions of "service-level agreements and uptime guarantees, data retention and privacy practices, support and maintenance, and customization options" then come up. What if private information is amongst the data sent up to a third-party Cloud Computing provider. What if the connection to the Cloud Computing provider goes down?
Also, there is the practical question of how exactly to connect internal infrastructure to Cloud Computing. Up to now, this has involved coding (e.g. see this dev guide for the Amazon SQS Service).
Vordel has produced the Vordel XML Gateway Cloud Edition which allows for connections to Cloud Computing environments such as Amazon and Force.com without coding, and including functionality such as stripping (or selectively encrypting) private data before it goes up to the Cloud provider, response time analysis, and data transformation.
This allows the hybrid "local and Cloud" model to be deployed:

Configuration is drag-and-drop, with no coding, as shown below. All of the filters which you can see on the right of the screenshot below (encryption, monitoring, caching) are available to drag-and-drop into the circuit which runs on the Vordel Gateway:
