automount nfs: autofs timeout settings for unreliable servers – how to avoid hangup?

I’m running a small server for our flat share. It’s mostly a file server with some additional services. The clients are Linux machines (mostly Ubuntu, but some others Distros too) and some Mac(-Book)s in between (but they’re not important for the question). The server is running Ubuntu 11.10 (Oneiric Ocelot) ‘Server Edition’, the system from which I do my setup and testing runs the 11.10 ‘Desktop Edition’. We where running our shares with Samba (which we are more familiar with) for quite some time but then migrate to NFS (because we don’t have any Windows users in the LAN and want to try it out) and so far everything works fine.