I recently upgraded to Ubuntu 12.04 (Precise Pangolin) and find Unity 5.0 unfamiliar and sluggish, so I would like to downgrade to Unity 4.0, that was included in Ubuntu 11.10 (Oneiric Ocelot). I can't find any working archives of Unity 4.0 and I don't know what to do anymore.
Oscar, you'd need to grab the source of Unity from Ubuntu 11.10 and re-compile it with the newer libraries in 12.04.
That seems a bit overkill. Perhaps just try unity-2d.