Hmm? My x86_64 CentOS 5 VM runs GNOME 2 in ~300MB. My Rawhide machine is close to ~200MB after booting runlevel 3. My F16 netbook is close to 150MB in the same state. Running X on top of that puts it over the VM's usage and I'm just running xmonad and xmobar. The lowest I've seen with Fedora (13 or 14 FWIW) is ~60MB on an i686 and pretty stripped down (no sendmail, sshd, iptables, etc.).
Now, of course, that's nothing compared to my FreeBSD box which boots in 30MB and rises to 40MB after running its jails which include nginx, postgres, a few fastcgi instances, git-daemon, and musicpd.