Server load high, CPU idle. NFS the cause?

you can try to use iostat to pin down which device generates the i/o wait:

# iostat -k -h -n 5

see the iostat man page for further details. nfs is often part of the problem especially if you serve a large number of small files or have particular many file operations. you can tune nfs access by using the usual mount options like rsize=32768,wsize=32768. there's a good whitepaper by netapp covering this topic: http://media.netapp.com/documents/tr-3183.pdf

also make sure you have no drops on the network interface..

hope this helps

frank.