How to install Gnome 3 on Ubuntu 11.04 and still have a stable system?

[Amedee Van Gasse]

For me, Linux is all about choice.
Suppose I wanted to install Gnome 3 on Ubuntu 11.04, how would I do 
that? I have done my homework and used Google, but everything I found 
involves adding ppa:gnome3-team/gnome3 to the repository, and included a 
warning that it will break Unity and that there was no downgrade path. 
But most of these things were at least 2 months old, so before 11.04 was 
released.
I really want to have my cookie AND eat it, iow when I log in I want to 
choose between Gnome 3 today, Unity tomorrow, KDE the day after and 
Fluxbox the day after that.

Anyone here who has successfully installed Gnome 3 on 11.04 and still 
has Unity?