NFS Security Problems - What are they? - Can they be fixed?

[ZZASSGL%cms.manchester-computing-centre.ac.uk at nsfnet-relay.ac.uk]

I am in the process of evaluating a Unix file server system using
tcp/ip and nfs.  The prospective users have heard stories of nfs
security being poor and this is putting them off using the service.
 
As far as I can see nfs is no worse than tcp/ip and Unix itsself
as far as security is concerned.  Is there something I have missed
and should particularly look out for?
 
Geoff.
Wot! No fancy signature?