Bug#551821: initscripts: fails to mount NFS shares at boot
I have the same problem and neither setting ASYNCMOUNTNFS=no in
/etc/default/rcS nor using bg as a mount option in /etc/fstab solves it.
Both of these lead to the following error message, though my server name
mount.nfs: Failed to resolve server server-name: Name or service not known
When I change the name to the corresponding IP address, the error is "No
route to host".
It seems that the network is not really up yet when
/etc/network/if-up.d/mountnfs is executed.