I used to think that multitenancy was a key incentive for Cloud Computing. The experience of the last couple of years leads me to a different view. The Cloud makes IT more ubiquitous, but multitenancy is far from being ubiquitous – so most of the services offered in the cloud are either not multitenant or use some kind of shared-hardware scheme (virtualization). So far there seems to be more cloud computing capacity than there is a demand for it – so the improved resource usage aspect is not so important. I also see that many enterprises adopt the Cloud advantages for their own software, for example rolling out core enterprise applications as RIA’s to their extended ecosystem partners and thus streamlining the supply chain and reducing costs.
My conclusion is that multitenancy is more of a future feature that would emerge when the economy would mandate it. So my recommendation is to adopt application platforms that enable multitenancy and develop future applications as such, and in the meantime take advantage of the Cloud using pragmatic approaches.