Per Its Time vSphere 5 Upgrade, time to upgrade VMFS datastores. Like the last couple of steps this one completed w/o issue. Note that it is better to create VMFS datastores because you'll get a 1MB block size regardless of what size datastore you're creating, optimizing disk space. Compare this to the 2-8MB block sizes required based on datastore size in ESXi 4.1 and earlier.
All of my datastores now report to be VMFS version 5.54.