I have two Fedora 15 machines, they both authenticate using NIS and mount home directories via NFS. The first machine worked perfectly, the second did not. I could login via ssh (nis works) but all my file owners were nobody:users.
Anyhow, through much trial and error I learned about
/etc/imapd.conf. So after booting my machine, if I restarted rpcidmapd and autofs then the file permissions were correct.
After much Googling I found this
edit /etc/idmapd.conf uncomment and edit Domain = <your nis domain>
If I had to guess, I think the NIS domain isn't being set until after rpc.idmapd and automount are started. That's why restarting the services later seems to work. Or whatever. Why it works on one fresh install but not the next I'll never know.