I came up against an issue mounting via nfs from a Linux host to an OpenSolaris virtualbox guest (see this post for automounting nfs on OpenSolaris). Checking the host's logs revealed the issue: mountd:  [...] refused mount request [..] illegal port.

This is seemingly caused due to the natted connection between guest and host. Adding (insecure) in the host's /etc/exports line for this export enabled the guest to successfully mount the nfs share.

Recently setting up a few Opensolaris NFS clients served from Linux exports, I encountered an error:

Jul 24 13:02:53 osolmobil.swatteksystems.com nfs: [ID 435675 kern.warning] 
WARNING: NFS server initial call to 192.168.0.64 failed: Not owner

To fix this, I added entries on the NFS clients like so within /etc/auto_master (unchanged) & /etc/auto_direct files:

/-  	/etc/auto_direct

/data		-onosuid,vers=3	192.168.0.64:/data