I have used Gnome-Shell built from source, with the nouveau drivers from the xorg-edgers PPA for Ubuntu. (https://launchpad.net/~xorg-edgers/+archive/ppa)
They are enable to use composite and gnome-shell worked really good with them. Gnome-shell was actually faster using nouveau rather than drivers from nvidia.

Since clutter1.2 was introduced I have never been able to run g-s.
A picture describes more than a thousand words:
http://picasaweb.google.com/lh/photo/mTwyG8AjvaWuCczBujHfkw?feat=directlink
It sort of runs but only on 25% of the screen. 

When I no longer could run the gnome-shell I had built from source I tried a PPA. It worked but yet again stopped when I had to upgrade to clutter1.2

Strange thing is, Gnome-shell works with the drivers provided from nvidia but it's superslow compared to nouveau.

Output from when I run ./gnome-shell --replace with nouveau.
tomas@hydra:~/gnome-shell/source/gnome-shell/src$ ./gnome-shell --replace
Panel leaving: a new panel shell is starting.

(gnome-panel:31317): EggSMClient-CRITICAL **: egg_sm_client_set_mode: assertion `global_client == NULL || global_client_mode == EGG_SM_CLIENT_MODE_DISABLED' failed

(gnome-panel:31317): GLib-GObject-WARNING **: instance with invalid (NULL) class pointer

(gnome-panel:31317): GLib-GObject-CRITICAL **: g_signal_handlers_disconnect_matched: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

(gnome-panel:31317): GLib-GObject-CRITICAL **: g_object_set: assertion `G_IS_OBJECT (object)' failed

(gnome-panel:31317): GLib-GObject-WARNING **: instance with invalid (NULL) class pointer

(gnome-panel:31317): GLib-GObject-CRITICAL **: g_signal_connect_data: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

(gnome-panel:31317): Gtk-CRITICAL **: gtk_widget_show: assertion `GTK_IS_WIDGET (widget)' failed

(gnome-panel:31317): Gtk-CRITICAL **: gtk_widget_show: assertion `GTK_IS_WIDGET (widget)' failed

(gnome-panel:31317): Gtk-CRITICAL **: gtk_widget_show: assertion `GTK_IS_WIDGET (widget)' failed

(gnome-panel:31317): Gtk-CRITICAL **: gtk_widget_show: assertion `GTK_IS_WIDGET (widget)' failed
      JS LOG: GNOME Shell started at Sun Mar 28 2010 01:43:53 GMT+0100 (CET)
^CShell killed with signal 2


MacBook generation 5,1 
GPU: 9400M
OS: Ubuntu 10.04 Beta1