They don't use virtualization for any of their normal infrastructure -- it's much more productive to have locality with GFS/BigTable/memcache/App/etc all runnin

They don't use virtualization for any of their normal infrastructure -- it's much more productive to have locality with GFS/BigTable/memcache/App/etc all running in the same OS image on every machine. I do see them having plenty of use for virtualization when provisioning machines to run non-infrastructure, their client software, other people's software, etc. Its usefulness for software testing should be obvious. I don't know if they use full x86 virt. for it, but your App Engine processes have several layers of OS sandboxing around them.