We are encountering the same issue. It has happened on three of our 12 ESXi 5.0 hosts in the past 2 weeks. Basically, perfromance on the VMs on the host becom sluggish and for brief periods of time vCenter is unable to contact the host. These gaps can easily be seen in the Performance->Advanced->System graph. Over a period of an hour or two the gaps of unreachable time get worse and worse. vMotioning of VMs begin failing with errors. Eventually the host becomes completely unreachable and requires a restart. After the host becomes unreachable, we are seeing the same issue where a restart from the console (F12) sits there and never completes, requiring a hard reset.
We upgraded all our hosts to v5.0 around 100 days ago and are just now seeing this phenomenon. It feels like it is related to a combination of uptime + load on the host. We have a ticket opened with VMware. Will post here as we discover anything.
