[alliem]

I only see an upvote button, what gives?

[Zimahl]

You don't have enough karma to down vote. There isn't a specific place that tells one what that karma is and I don't have the answer since I still can not down vote either.

I've heard it's the flat-rate karma of 500. I've also heard that it's a moving target based on how many users or how much karma is currently out in the world.

If it is calculated and not flat, it specifically hurts new users while giving older users more power.

[alliem]

So a downvote button is an unlockable, interesting. Where did you learn this?

[Zimahl]

It's in the FAQ (http://ycombinator.com/newsfaq.html).