Ran across a new problem today after having a NAS device auto-update it's firmware.  All of a sudden Solaris clients couldn't connect over NFS anymore.  Oddly enough, Mac NFS clients still could!  After hunting around for awhile I finally found some references to NFSv4 being broken (as in advertised, but not actually supported) in the newer Linux kernels.  I guess that NAS device is Linux based and the update included a newer kernel!  Also appears that the Mac must not support v4 yet, since it kept working?  Restricting Solaris to ignore advertisements and just use v3 solved the issue.  You can either edit your nfs defaults file to set v3 for the entire system (the recommendation I found online), or you could just do what I did and throw a "vers=3" onto the options field in the vfstab...