So, I got the kerberized NFSv4 home directory to work - until my ticket expires. The screen saver attempts to access my home directory and just sits there and waits. So I don't get the enter my password and cannot renew a ticket. There are a number of posts around
Ubuntu seem to have patched the kernel: bug 1014910 and bug 794112. I am not convinced this is the correct behaviour.
in this post the possibility to zap the kerberos cache files is discussed which might be an option