graeme_p - 6:59 am on Sep 27, 2013 (gmt 0)
You do not need dual boot to have multiple Linux desktops. You just install the desktops from the software installer and choose between them when you login (rather than at boot).
You can install the Pantheon desktop from Elementary on top of Ubuntu, and you can do the same with MATE, XFCE etc. Bodhi Linux does not support this - but if you like experimenting you could start with Bodhi, and then install Unity (the ubuntu standard one) and the rest on top of it.
At the moment I have Ubuntu Unity and MATE installed (but I always use MATE) and I am thinking of trying Pantheon.
I would like to hear how Bodhi Linux works out for you after a few weeks. Its been a while since I tried Enlightenment.
For the POS machines, you do have the option of locking down employees access to only the POS application. It also seems a good place to use a really minimal desktop like LXDE, IceWM or Openbox.