I've installed every version of Ubuntu released in the last four years and enjoyed it getting more and more user-friendly. I was so comfortable with it that I removed windows XP from my father-in-law's laptop and replaced it with Ubuntu about a year ago. I had to spent a couple of hours with him to set him up but that was all to it. He has been using it happily since then.. And I have the piece of mind as I am no longer worried he will be getting malware / viruses on his laptop which is connected to my home network.
At the end of April, Ubuntu released 11.04. I upgraded my laptop but left his laptop alone. Ubuntu 11.04 release brought a radical GUI change named Ubuntu-Unity. Personally, I did not find it too difficult to use although it did not seem to me that it made things any easier than they used to be.
Today, we upgraded my father-in-law's laptop to Ubuntu 11.04 as well. I let him use it for a while and it's been absolute nightmare for him. He hated the new interface, it was way too confusing for him. One of the reason for the new interface was to simplify the interface and make it easy to find things. Unfortunately, his experience was exact opposite. So, I rolled him back to Classic Ubuntu (Gnome) interface. You can find detailed instructions here to roll back.
"The new, highly simplified desktop interface “borrowed consciously” from “other successful platforms,” including Windows and Mac OS X, Shuttleworth said." according to eweek.com.
So, I will have him try OS X to see if he is going to have the same challenges. If he can use OS X just fine, then maybe these borrowed ideas were not implemented well enough in Unity.
Update [08/01/2011]: He found OS X easier to use than Unity.