Why is udev renaming my network interfaces?

It was driving me nuts. I was setting up a few virtual servers and the network interfaces were not showing up. I looked in dmesg and there were some odd lines that looked like this.

udev: renamed network interface eth1 to eth2
udev: renamed network interface eth0_rename to eth1

It turns out that udev that takes care of matching up the network interfaces to the physical hardware so the same hardware will always get the same device ids. So, in order to save myself time, instead of installing the Ubuntu again on each VM, I just copied the HD from one machine to the next. The old VM had different MAC addresses for the interfaces saved in the udev config. So, with the help of this post, I deleted /etc/udev/rules.d/70-persistent-net.rules and it stopped doing the rename.