Ask HN: Capacity Planning in the Cloud: An Oxymoron?

Obviously, there is some sarcasm in the question above. Arguably, the cloud's greatest benefit is its elasticity, which implies that most aspects of traditional (focused on own or rented hardware) capacity planning for the cloud environment are not really applicable. However, clearly, some capacity planning is still needed, both for initial deployments as well as for ongoing operations. So, the real question is: "What are the optimal strategies, tactical approaches, potential issues and best practices for capacity planning in the cloud?". Comments and/or points to relevant resources are welcome.