Three times, once in the graveyard in GOF. < /pottergeek> :)
I stand corrected. I just didn't think that Voldy would count that one since 1) Olivander explained why the twin wand cores would cancel each other out and 2) Voldy didn't get knocked on his butt that time.
Speaking about Pottergeeks, it's pretty pathetic that we are discussing what two fictional characters were thinking during their (potential) last moments on Earth.