Killzone 2 leaderboards aren't just for tracking who's best at putting down Helghast scum (or the invading ISA, if that's how you roll). The leaderboards are also handy for when you need to keep track of a milestone, like Killzone 2's millionth player to log in online, for example.
That's right, Killzone 2 has over one million folks taking the fight online, achieving the number in little over two months of being on store shelves. Based on sales data, this also means that roughly 2/3rds of the people that purchased the game have taken it online, which is impressive in and of itself. And with so many of the people that bought the game going online to try their skills against the rest of the world, we're willing to bet that Sony will sell a good deal of Steel and Titanium to gamers.