On my part, I haven't had serious trouble with SMB mounts. I get the spinning wheel if I forget to unmount it, but I generally can get access to the "eject" if I am a little patient. I get however the same kind of *serious* problem with NFS mounts as the one described in this thread for SMB moutns. I found that NFS mounts are generally a killer, if I forget to umount them before I get offline or change subnet. In fact, about 99% of my forced reboot (often by having to power down forcefully) is due to this NFS mount problem. As described, the computer locks up, apps after apps, until the system is completely locked up and a forced powerdown is my only solution.
Apparently, soft mounts do not solve the problem (not extensively tested as I only got the hint from this list yesterday), but I'll experiment some more (thanks for the trick provided in this thread).
I am using mount_nfs -i -b -s ..., may be I need to explicitely specify a timeout with -x or -t ?