I tend to switch back and forth from different environments within the *buntu ecosystem but I was wondering if I could just install all of the Desktop Environments onto Ubuntu 11.10 and be able to switch to them if I wanted to.
There is nothing really stopping you installing multiple desktop environments. It is safe to do so.
However - the key issue is that every environment comes with its own set of default applications. This can leave your menu very cluttered with applications from each environment where the application hasn't been specifically limited to one particular desktop.
I personally have multiple virtual guests, each with a single desktop distro and all linked with common folder to enable sharing of files. I can then hop between distro's very quickly all from one desktop without logging out and in.