I have been troubled for hours by some problems, so now i share something with you, so that you have an easier life.
In short if you want to remove unity in Ubuntu 11.10 remove all packages named *unity* from the ‘Ubuntu Software Center’
except: libunity6 and unity-greeter !!!!
If you use lightdm for login screen and you remove unity-greeter then at boot time your system will freeze!
If you use gdm then you can remove unity-greeter without problem.
In addition if you remove libunity6 then nautilus is also removed because it has it as a dependency.
Nautilus is the program that is responsible for opening your folders and showing you their contents when you click on them and generally it’s like the explorer in windows systems.
PS. Just in case you are stuck in command line and you are a novice user in ubuntu just make sure you install again the removed packages:
$sudo apt-get install nautilus