The term describes something that is exceptional, or awesome. It is derived from "pwn" which is ultimate nerd internet ownage. To own ponies is to do something amazing or be amazing.
The reverse of this, sucking, is to "blow ponies".
1)If something owns heads it is supposedly really good, sublime even.
2) ...delivers the Murkle Circle
3) beats/owns people
4) ...opens a can of whoop-ass on your head