its never happened to me but i play halo 3 a lot and i sumtimes play with friends that like overloading hte maps and that just makes the chances so much higher of getting the ring of death.
oh and sumtimes i think mods of maps can also make the chances higher for example the map on sandtrap 99 elephants that map is SOOO laggy even with one player
I personally don't own a 360 but my neighbor who does says the rings of death happen mostly when people don't leave room around the 360 for the fans to work properly.
they should make them beter like the ps3 so they dont break as easy they have a 20 percent chance of breaking when a ps3 has a1 percent chance of breaking