Not all IT realms work well in the virtual environment currently. For instance, in the backup realm, virtualization of a backup server can be troublesome. One way that might be a better way to utilize the virtual only environment in backup infrastructure, might be to use multiple virtual backup servers to backup multiple different machines on the network. I have not seen this in production, but hypothetically, having a coordinated set of virtual backup machines backing up multiple machines (physical and virtual) and then storing that data in a coordinated system might be an answer to the problems of traditional backup in virtual environment and scalability.
To bring the point back to this topic, I think that perhaps the virtual environment becomes a matter of recongizing the limitations of virtualization and then finding a way to scale within those limitations as there are certainly benefits to having a virtual only infrastructure.
Full Disclosure: I have a tech role at backup software vendor, Arkeia Software.
