Ok perhaps it isnt "International Update your VMware Templates Day"
However as VMware admin it is too easily left of the upgrade list.
Normally when moving from, for example ESX 4 to ESX 4U1, the procedure is this:
1) Update VCenter
2) Update ESX hosts
3) Update VMs (vmware-tools)..then VM/HW version
But do not for get templates!
I recently bumped into a case where an old version of vmware tools (from ESX 3U3) was causing issues being deployed. It started with a Blue screen of death "PFN_LIST_CORRUPT" then programs crashing/not responding.
It was tracked back to an old VDI Windows XP 32bit image using a very old version of vmware tools.
Once the Template was upgraded the issue was fixed!
p.s. if you want to upgrade vmware tools on multiple hosts without rebooting your production boxes..look here