I can confirm this activity as well after a recent overhaul of my home network. It's very frustrating - NFS usage will cause client lockups. This has happened several times, and can only be resolved by pressing the hard reset button. It happens one of two ways: X locks up completely, or X stops responding but I can move the mouse. In the second scenario, pressing Ctrl+Alt+Fn will lock up X completely.
As a symptom of the problem is a lockup of X, I will mention that I am using the NVIDIA driver. I will test later without the proprietary driver to see if this effects anything, though lockups only occur during some NFS activity so doubt this is responsible.
Locks occur all the time:
When populating my shotwell library (Photos stored on server)
Nautilus getting screenshots of HD videos
Transfer of large files.
Even just updating my .mozilla profile
Crashes are easily reproducable (Basically any time I use NFS).
My desktop is using a gigabit card, as is the server, and they are connected with a netgear gigabit switch. I will post some stats about hardware on the machines later today, as well as info from nfsstat -m and mount.
Server is Ubuntu-server 10.10
Desktop is Ubuntu 10.10
I have another machine on the network which uses a 100mbit card and so far I have yet to see a crash when using NFS, but I haven't performed any serious tests yet. This machine is also using Ubuntu 10.10.
If there is anything specific I can provide please let me know.