When Arthas was a Paladin, he held his hammer in his right hand. When he got Frostmourne, he held it in his right hand. However, when he became evil, he held Frostmourne in his left hand! I think Blizzard goofed.
Gotgunz is right about 1 thing.. he is a frickin show off...
but i wanna ask yall a question : does anybody here ride a horse ? or ever rode 1 ? i was tought sumthin while i had horse ridin courses... u hold the reins with ur stronger hand... that's all i can say bou the death knight holding frostmourne in the left hand... now for when he got frostmourne while still a paladin and holding it with his left hand... well that may just be a change of model..