Comment 13 for bug 903382

apt-cache show is showing you that gnome-shell is in both the "oneiric" repository (which is frozen when oneiric was released) and the "oneiric-updates" repository. Try running apt-cache policy gnome-shell to see which one is actually installed.

I don't have a powerpc machine so this is difficult for me to test but I believe it's working as the original bug reporter confirms.