I'm not sure since some of the "optional packages" in Pirut are "Default" packages in the group:
Code:
yum groupinfo "GNOME Desktop Environment"
Loading "installonlyn" plugin
Setting up Group Process
Group: GNOME Desktop Environment
Description: GNOME is a powerful graphical user interface which includes a panel, desktop, system icons, and a graphical file man ager.
Mandatory Packages:
nautilus
esound
control-center
yelp
gnome-terminal
gnome-panel
gnome-applets
gnome-session
metacity
Default Packages:
tomboy
gnome-user-docs
vino
gnome-themes
xdg-user-dirs-gtk
gedit
gnome-power-manager
evince
gnome-system-monitor
compiz
alacarte
gnome-backgrounds
at-spi
gnome-volume-manager
scim-bridge-gtk
gnome-bluetooth
gok
gnome-audio
gstreamer-plugins-ugly
dvd+rw-tools
nautilus-cd-burner
esc
notification-daemon
gnome-user-share
gtk2-engines
NetworkManager-gnome
desktop-printing
im-chooser
gnome-netstatus
bug-buddy
file-roller
nautilus-sendto-bluetooth
gnome-utils
gnome-pilot
fast-user-switch-applet
eog
gnome-screensaver
gnome-media
gnome-vfs2-smb
gcalctool
gthumb
nautilus-sendto
orca
Optional Packages:
gnochm
tracker-search-tool
tango-icon-theme
hal-gnome
gnome-applet-timer
nautilus-flac-converter
gtweakui
gnome-commander
gnome-themes-extras
istanbul
nautilus-search-tool
glipper
rss-glx-gnome-screensaver
glunarclock
gnome-applet-sensors
gconf-editor
xscreensaver-gl-extras-gss
wallpapoz
dasher
sabayon
beagle-evolution
nautilus-actions
xscreensaver-extras-gss
gnome-applet-music
byzanz
nautilus-open-terminal
themes-backgrounds-gnome
gnotime
gmpc
gimmie
gdesklets
gnome-keyring-manager
wp_tray
beagle-gui
seahorse
gnome-pilot-conduits
panelfm
buoh
gnome-theme-clearlooks-bigpack
tango-icon-theme-extras
lock-keys-applet
nautilus-image-converter
deskbar-applet
verbiste-gnome
beryl-gnome
gnome-applet-netspeed
You will lose basic stuff like gedit and NetworkManager and just be left with the Mandatory packages listed above.
If you're sure that's what you want then you can just right click on "Gnome Desktop Environment" and select "Deselect all optional packages", for a minimal Gnome environment.
You can always reinstall any packages afterwards if you miss them.