Real world example of moving 100% to the cloud
Cloud architecture isn't dramatically different than on-premise, though some inherent advantages make it a worthwhile deployment option.
Examples of architectures designed to run on Amazon Web Services are a great way to illustrate the necessary design changes and patterns associated with a cloud deployment methodology.
Soocial.com, a "one address book solution to contact management" runs entirely on AWS and uses some interesting technologies to make their service work, including RabbitMQ, an open-source implementation of AMQP, the emerging standard for high-performance enterprise messaging. (I've written about AMQP and RabbitMQ here, and here in the past.)
One of the most interesting things is how the architecture isn't dramatically different than it would be if you were to build an on-premise version--except that Soocial is able to take advantage the Amazon Web Services EC2's scale, hot-standby, and backups. It's definitely worth learning more about if you are interested in the cloud.