VMware has posted an updated blog on their new VMware vSphere 5 licensing model. The vSphere licensing model pdf can also be downloaded.There are three factors that are key to vSphere 5 licensing:
1. Number of VMs2. Amount of vRAM per VM3. What vSphere 5 edition you are running due to the entitlements for different editions per the entitlement resource.
VMware Technical Marketing team has written up a blog post with tool to help people add the total amount of vRAM allocated in VMs. Updated as of August 2011, the Official VMware License Advisor is now available for download.