Here is a patch I've been using for quite a while now
that will zero out the nfs stats on both the server
and client side.

There are two interface: nfsstat and /proc.
The nfstat interface looks like (from the manpage):
-z     Zeros out all or some of the statistics. Typical uses would be:
     nfsstat -z  - zeros all statistics
     nfsstat -zc - zeros only client statistics
     nfsstat -zs - zeros only server statistics
     nfsstat -zr - zeros only RPC statistics
     nfsstat -zn - zeros only NFS call statistics

Note: the nfs-utils in the Fedora Core 2/3 release already have
this support.

The /proc interface look something like:

echo nfs > /proc/net/rpc/nfs[d] # zeros calls stats
echo rpc > /proc/net/rpc/nfs[d] # zeros rpc stats
echo net > /proc/net/rpc/nfs[d] # zeros connection stats
echo rc  > /proc/net/rpc/nfsd   # zeros server cache stats
echo fh  > /proc/net/rpc/nfsd   # zeros server fh stats

Again this is a patch I've had kicking around for sometime
so its pretty well tested... and I'm a bit dependent on it
in the sense its annoying when I go to zero the stats
and I can't because I forgot to apply the patch...

I'm hopeful that other people will also find this patch useful
as well and it will make its way into an upstream kernel
in the very near future....

SteveD.