Vmware is like Windows
Seeing as you get better IOOP's and more flexibility with KVM why do the masses use VMware - which has less features and still to this day involves being windowscentric to use (the webGUI sucks)
Things that cost £1000's in license fees (i.e HA/clustering) is free in KVM/Ovirt
There are many thing you can do in KVM that are just not possible or are a PITA on Vmware.
i.e try resizing the first partition of a virtual disk image in VMware... (i.e /dev/sda1) when /dev/sda2 exists.
in KVM you can resize the first partition easily using virt-resize, you can also expandthe disk image, the LVM partition and underlying ext filesystem with one command (no twating about with parted/fdisk, etc)
virt-resize --expand $resizedisk --LV-expand $lvm /var/lib/libvirt/images/$Servername.img /var/lib/libvirt/images/$Servername.img.tmp
This is just a little thing of course but the most I use vmware the most I find it less flexible (and slower) than KVM.