For me, I use multiple operating systems daily on my computers and phones/tablets. Most of the time I carry two phones with me (usually some Android device and an iPhone).
I built three computers to run three separate operating systems. My main rig is my PC/Windows rig. I also run a Hackintosh rig and a *lower-end* rig for Ubuntu.
For phones, I have a box of "dumb" phones still lying around somewhere. Then there's the Nexus S, Galaxy Nexus, GS2/3, Note 1/2, Inspire, Droid DNA, Razr Maxx, One X, iPhone 4/4S/5 and a Z10. Yes, I do need to sell off a bunch of these...but I would much rather keep them. Most of the time, I'm carrying my DNA or Note 2 along with the iP5 but from time to time, I also like to use the Z10.
For tablets, I mainly use an iPad 4 but I also have a TF700, Nexus 7 and 10 lying around.