Comment 1 for bug 384347

I quote from the mount(8) manpage:
"The filesystem resides on a device that requires network access (used to prevent the system from attempting to mount these filesystems until the network has been enabled on the system)."

This isn't working in Ubuntu 9.10 either. _netdev is not honoured, while it should solve some problems.
Here's how I tested. /etc/fstab:
    coolio:/home /home nfs4 _netdev 0 0
    coolio:/Xchange /srv/xchange nfs _netdev 0 0
    coolio:/software /srv/software nfs _netdev 0 0
At boot, the usual messages appear (see also bug #504224)
(ESC for recovery shell)
/home: waiting for coolio:/home
/srv/xchange: waiting for coolio:/Xchange
/srv/software: waiting for coolio:/software

After that, nothing. Booting is unsuccessful (That is probably bug #470776)
In the recovery shell, you can see that the network is not up yet. (It comes up after a while.)
Now, _netdev was declared in /etc/fstab, so mountall should have waited for the network before trying to mount the filesystems. This would result in a successful boot.