OVF doesn't work
.. At least with vmware.
It's a great idea to allow interoperability between hypervisors. As the article says, the knowledge needed to convert between formats is well known and ovf was intended to be the standard to enable that. However, when the best known play only pays lip service then you have to ask what's the point...
Create a vm in virtual box and export as an ovf. Now try and import into esx or (shudder) vcloud. Even though all the required information is present in the ovf, vmware refuses to register the vm. You need to read the hardware details from the ovf, manually convert the virtual disk and manually create the vm. Btw, the import tool can clearly parse the ovf configuration and the disk conversion tool is part of esxi.
I hope that people have it better in the hyper v and xen space but from my experience ovf has failed.