Literally just deployed a pair of new OmniOS NFS servers last night, for high-availability hosting. We also serve VM storage from a pair of Illumos ZFS boxes over iSCSI.

We switched most of our primary NFS storage pairs from Linux to Illumos a good five years ago due to a bunch of locking issues and race conditions with high-volume NFS traffic. Solid as a rock as long as you have the right HBA heh