I have installed archlinux with gnome-shell and replacing ubuntu11.10 due to gvim's python issues for a couple days.

As I have tried them both. here is my Yet Another Compare between gnome-shell and unity.

Looking:
    Gnome-shell is cleaner at first glance. but you can make unity with that
looking.
    the notification and tray applet of gnome-shell is better than unity.
    gnome-shell is a bit stylized than unity which need a bit config with
compiz

Usablity:
    They both introduce a quick way of opening applications: Activites and
Dash.
    gnome-shell combine window ,desktop and applications in Activites which
looks cleaner.
    unity don't have window in dash. and you could config expo/scales with ccsm
to have similar using as gnome-shell does.
    And both works fine with easystroke. that's enough for me.
    
Configurability:
    gnome-shell have no config tool. only a install tool with gnome-tweak-tool
and gnome-shell-extension
    unity configs in ccsm. but not fully configured.
    
Stability:
    unity is stable enough. and it can automatic recover after crashes most of
the time. you can use unity --replace to recover it manually.
    gnome-shell (3.2.1) crashes more often. and should recover it manually.
    by gnome-shell --replace
    or DISPLAY=:0 gnome-shell --replace & in other tty
    and sometimes you can't react with the windows even with gnome-shell
recovered.
 
Conclusion:
    unity is easy enough to use and need some time to config.
    gnome-shell is elegant but need some time to get used to (it's
crash).