If you are using OpenSolaris and NFS for your datastores and using ESX you need to share out your zfs filesystems with anon=0 since ESX wants to write to the NFS datastore as root.

zfs set sharenfs=anon=0 usbpool/virtuals

I wouldn't mind having stuff like this if I could figure out how to properly get logging of the issues/connections in OpenSolaris. Anybody know how to increasing logging for the NFS services in OpenSolaris?