[walid]

You need more karma points to see a down vote button.

[DanBC]

The current threshold is, I think, 750 to get downvote for comments.

There's no downvote for submissions, but there is a flag button. I don't know if there's a karma threshold for that.

[mhofstadt]

Wow, I had no idea it was possible to earn your way up to a down vote button. Looks like I need to participate more. =)