It seems to be a good idea to make NFS mounts soft and interruptible on OS X. If a server disappears, or you disconnect your laptop, your machine is royally screwed if you touch a hard mounted file system. Finder will lock up waiting for a response from the server, and you will lose the ability to launch new programs via Finder, you won't be able to unmount, and you won't be able to reboot (even with /sbin/halt).
So I use the automounter and specify the -i and -s flags to enable interruptible and soft mounts. This solution may not save you from the Finder locking up (you'll have to wait for the soft timeout), but if you have Terminal running, you can terminate stalled programs, such as the Finder.
But I discovered a memory of sorts in the kernel ... mounts once mounted as hard mounts will not demonstrate the behavior of interruptible or soft mounts when remounted. A reboot is required. Umounting and then remounting does not prove sufficient.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021025071155959