VMWare works right out of the box with no user manual even needed. That's already more than can be said for any of the competition.
Not so sure about that last sentence there.
I trained a new hire to use VirtualBox on an Ubuntu 12.04 box this week. He had just about zero experience with virtualization. Basically my instructions were to have installation ISOs for whatever OS he wants to run virtualized and to apt-get install virtualbox. He then set everything up on his own and only asked for help when it came to setting up a virtual network. I told him he should first figure out cloning. A few minutes later we were back on the virtual network. My own experience a couple of years ago was similar. In both cases, we had the manual handy, but never used it.
My proficiency with KVM/libvirt took more effort. But virt-manager makes it pretty straight-forward. Our KVM/libvirt virtualization system has several host nodes running a few dozen guests with storage on a SAN/NAS (it does both). This wasn't painful to do at all. An automatic backups/snapshot system has been more challenging, but that's mostly just because we want to minimize interruption of the guest (just suspend the guest, grab an LVM snapshot, wake the guest, copy the snapshot, free the snapshot) and due to our larger guests being about 200GB in size. Storing versions of files that large, and moving them around, requires delta compression. (Hint: Use xdelta3 before copying the data off-site.)
We also played with Proxmox a few months ago. A summer student had all of the above (except for backups) working in two days. Confusion over whether the licensing was really free, the fact that it is its own distribution (a double-edged sword for sure), and the fact that configuration of aggregate network links (LACP) was really goofy, all kept us from adopting it. Too bad, being able to switch a guest from one host to another in real-time while viewing the guest's display with only a tiny pause, was a really neat trick.
If I can do the above mixed in with all of my other responsibilities (as a school authority director of tech), anyone can.