Here for what it's worth is the set of gnome packages that are currently in tasksel's desktop task. A gnome metapackage could include more. I would suggest not going overboard; if the metapackage becomes too big then it becomes subject to the same problems task packages used to have where it was easy for them to break if a package was removed from unstable due to bugginess or whatever. Also, everything in the metapackage will need to freeze with tasks+standard (assuming tasksel begins to use the metapackage).
# TODO: we really should have gnome meta-packages, which this # task could just pull in, rather than having to track all gnome here. gnome-session gnome-panel gnome-control-center imlib-base gnome-terminal gnome-applets gmc esound gnome-users-guide gnome-help gdm gnome-utils (Gimp is in that list too, but it's not really part on gnome AFAIK. So's abiword.) -- see shy jo

