Dealing with local storage is not very much different than a data center deployment. However, EC2 provides an interesting solution. Through the use of EBS storage, you can prevent data loss when an instance fails. Writing Couchbase data and configuration to EBS creates a reliable medium of storage. There is direct support for using EBS within RightScale and, of course, you can set it up manually.
Using EBS is definitely not required, but you should make sure to follow the best practices around performing backups.
Keep in mind that you will have to update the per-node disk path when configuring Couchbase to point to wherever you have mounted an external volume.