I'm not 100% sure how --noconfirm is supposed to work, but I tried it with -Su. I have several packages waiting to be upgraded. Here's how it went:

[root@localhost root]# pacman -Su --noconfirm

Targets: apache-2.0.50-3 atk-1.7.1-1 esd-0.2.34-1 filesystem-0.7-1 gimp-print-4.2.7-1 glib2-2.4.4-1 grub-0.95-2 gtk2-2.4.4-1 initscripts-0.7-2
libxml2-2.6.11-1 libgpg-error-0.7-1 libgcrypt-1.1.94-1 libxslt-1.1.8-1 neon-0.24.7-1 startup-notification-0.7-1

Beginning download...
[root@localhost root]#

At this point, everything is over. A line has been added to the pacman log saying "starting full system upgrade", and nothing more. This looks like a bug to me.