Well, I used to play the shit out of Dynasty/Samurai warriors when I was a wee lad, so I'll go with around 500,000 to 1,500,000. I know thats a really wide range, but 500,000 sounds like the bare minimum, and 1,500,000 sounds like the max.
Keep in mind, I used to play Konami games, so I would slaughter around 2,000 enemy's a match.
Plus, you haft'a add the rest of the enemy's from about 8 years gaming experience. (Been gaming since the PS one)
Also, I used to play games like Company of Heroes and Black and White.
But overall, my career probably spans 500,000 to 1,500,000.
Edit: Well hell, now that I'm thinking about it, I have recalculated that the number is over 6,000,000.
Then again, I'm bad with numbers. Seriously. I have repeated Algebra six times.