OpenStack tries to support too many different backends for most components and is a consultants' wet dream when it comes to custom work and patches required that can be readily milked into an expensive and lengthy deployment, as well as expensive post-deployment maintainence and upgrades. It's only that at a significant (Netflix) scale can the costs of DIY be cheaper than just paying the AWS tax. (Last I heard, Yahoo employed a team dedicated to maintaining OpenStack. Also, I hear from others that this is the norm, not the exception. We looked at OpenStack at Stanford, but there are other IaaS clouds that have better opinions about architectural choices (only supporting say Xen and Vmware because they're production proven) and less code.)