I stopped providing KVM VPS completely over time and only retained existing customer. Main reason, dealing with CPU/IO abuse and customers who refuse to admit they are using sufficient resources to warrant a dedicated server. I used to charge more for KVM, and still profit wise it's nowhere near OVZ nodes but yet I have to deal with more KVM customer issues in a single node vs OVZ which has at least twice the number of VPS.
OVZ CPU abuse I can just save a copy of the CPU graph for the VPS itself or point the customer to it, and pretty much no argument, graphs and numbers don't lie. KVM I literally have to go back-forward with the customer multiple times because they'll never admit to CPU abuse or simply don't know how to fix it and I have no easy graph to slam on the table and go "look here". IO usage on KVM is worse too, customers don't know/want to use virtio and result in massive IO abuse especially for Windows, I'm guessing swap usage.
Might be just unique to me since majority of my customers are from the Asia region, my US/EU KVM customers don't have as much abuse issues or are at least able to identify and rectify quickly.