Is the OS X firewall blocking nfs?
How are you mounting the export? If you're not trying it from within Terminal, does it work from within it? ______________________________________________
The OS X firewall dos not appear to be a factor. Actually it works just fine when I turn off the firewall on the CentOS end.
Could it be that even when I am trying to mount over the TCP the NFS client on the Mac OS X side still tried to connect to some UDP port? I am asking that because everyone else mounts just fine with the firewall up on the server end.
Boris.