cat >/dev/null_

(UPDATE 20100302)

I wanted to change the default runlevel on my 9.10 Netbook Remix to 3, hoping to get a text-only login prompt.
I knew about the switch to upstart, so I did a bit of googling and I found this page, instructing me to change DEFAULT_RUNLEVEL in /etc/init/rc-sysinit.conf.

But, after switching to default runlevel 3, gdm was still popping up.

That’s when I noticed this in /etc/init/gdm.conf:

start on (filesystem
and started hal
and tty-device-added KERNEL=tty7
and (graphics-device-added or stopped udevtrigger))
stop on runlevel [016]

Adding runlevel 3 to the stop on directive did the trick, but apparently only when I passed the runlevel via bootloader.
The correct action was to specify the exclusion of my new default runlevel on the start on directive.

To sum it up:

in /etc/init/rc-sysinit.conf:
env DEFAULT_RUNLEVEL=3

in /etc/init/gdm.conf:
start on (filesystem
and started hal
and tty-device-added KERNEL=tty7
and (graphics-device-added or stopped udevtrigger)
and runlevel [!3])
stop on runlevel [016]

Gotta love this transition to upstart!!!

Update: this seems to work on 9.10 desktop.