Before you go updating your vSphere to the new 5.1 version that was just released, VMware had just released this alert yesterday (9/12) that vSphere 5.1 is currently NOT compatible with any version of VMware View.
vSphere 5.1 is in the process of being certified against VMware View. We recommend that you do not upgrade vSphere above the supported versions listed in the VMware View 5.1 Release Notes.
For further updates and more information on this alert, refer to KB article:
vSphere 5.1 is not compatible with any versions VMware View (2035268).
If you don’t use VMware View, and are ready to upgrade to vSphere 5.1 be sure to check out the Installing vCenter Server 5.1 best practices from VMware.