Gabrie van Zanten posted another great article detailing the impact of Large Pages and Transparent Page Sharing on memory usage in a VMware environment and how these technologies make it more difficult for an admin to monitor real free memory on an ESX host.
When Large Pages are enabled in the guest OS and the VM is running on a host that supports Large Pages, ESX will not perform Transparent Page Sharing on the VM’s memory. The result of this behavior is that it becomes more difficult to see how much free memory you have in your environment. In short, using Large Pages is a trade-off between memory savings and performance benefits.