Here are some vSphere 5 issues. Be aware before upgrading to vSphere 5:
Update 03-11-2011 VMware released a patch that solves this problem. More information can be found here.
– HP BladeSystem – Emulex be2net Inbox Driver Version 18.104.22.168 Does Not Support Flex-10 or Flex Fabric Adapters on VMware ESXi 5.0 in a Virtual Connect Environment and Emulex OneConnect driver not supported on vSphere 5.0 for HP hardware
Update 02-11-2011 HP has a new firmware and driver to fix this problem. More info can be found here.
– VMware ESXi 5.0 – Unable to Add Host to vCenter After Applying a VMware License to a Host Running the HP Custom Image for VMware ESXi 5.0