I ran into a problem using my Mac with my CentOS NFS Share.
I was able to connect but everytime I tried to upload the connection was lost and the device was unmounted. After some research I found that you must have firewall turned off on your mac to have correct NFS communication.
Go to: System Prefernences -> Security
And turn off your firewall. I am not happy with this but i am behind a second firewall while i am using my nfs share.
Some more information about this issue: http://discussions.apple.com/thread.jspa?threadID=1531867