vCloud Air is VMware’s public cloud offering, similar to Amazon’s AWS or Microsoft’s Azure. The key distincion between vCloud Air and these other offerings is that vCloud Air uses VMware’s products such as vSphere.
The VMWare User Group (VMUG) recently added free credits on vCloud Air OnDemand as part of their EVALExperience program. As the name suggests, vCloud Air OnDemand is a pay-as-you-go service. I looked at this service offering as a server engineer with a reasonable background in VMware, considering aspects such as the ease of basic tasks, general administration, technical considerations for the business (good and bad) and how it compares to other offerings.