When we started over 5 years ago, we had a small ESX 3.x cluster and did many P2V (Physical to Virtual) conversions.
Over the next 4 years we virtualized 20-25% per year with P2V until today we sit at about the 90% virtualization level in our datacenters with 21 ESXi hosts backed by 20Tb of storage all on a 10Gb network.
Now the frequency of P2Vs as decreased as we now persuade customers to go directly virtual with their new projects by buying a piece of VI (Virtual Infrastructure) - essentially "growing the cloud".
Recently we had a customer who had already purchased their hardware and it had substantial warrantee support remaing - so we decided to:
P2V the existing webapp to the VI
P2E (Physical to ESXi - install ESXi over the old OS)
V2E (Virtual back to new ESXi - storage vMotion)
The only interruption was 10 minutes while the webapp was suspended to do a clean P2V.
The customer was happy to have the virtual space to create dev instance VMs and we were happy to continue to add capacity to our VI (and grateful for the flexibility virtualization provides to accomplish these kinds of migrations)