Stackoverflow already has a pretty solid reputation system with pseudonymous users.

What it means is the bar for becoming a new StackOverflow contributor (or Reddit admin, or Wikipedian) might become much, much higher. "Oh, you want to contribute your first post? Show me the bicycles in this image, find the letters in this image, and provide the names of two existing Stack Overflow users with over 1000 karma who can vouch for you, and also you see a tortoise on its back, baking in the sun. You're not helping it. Why aren't you helping it?..."