For the purposes of this discussion, we will refer to "the cloud" as Amazon's EC2 environment since that is by far the most common cloud-based environment. However the same considerations apply to any environment that acts like EC2 (an organization's private cloud for example). In terms of the software itself, we have done extensive testing within EC2 (and some of our largest customers have already deployed Couchbase there for production use). Because of this, we have encountered and resolved a variety of bugs only exposed by the sometimes unpredictable characteristics of this environment.
Being simply a software package, Couchbase Server is extremely easy to deploy in the cloud. From the software's perspective, there is really no difference being installed on bare-metal or virtualized operating systems. On the other hand, the management and deployment characteristics of the cloud warrant a separate discussion on the best ways to use Couchbase.
We have written a number of RightScale templates to aid in your deployment within Amazon. You can very easily sign up for a free RightScale account to try it out. The templates handle almost all of the special configuration needed to make your experience within EC2 successful. Direct integration with RightScale also allows us to do some pretty cool things around auto-scaling and pre-packaged deployment. Check out the templates here Couchbase on RightScale
We've also authored an AMI for use within EC2 independent of RightScale. When using these, you will have to handle the specific complexities yourself. You can find this AMI by searching for 'couchbase' in Amazon's EC2 portal.
Some considerations to take into account when deploying within the cloud are:
Local storage being ephemeral
IP addresses of a server changing from runtime to runtime
Security groups/firewall settings