[SomeCallMeTim]

Downvoting does more than that. It can hide a discussion, and regardless, it certainly buries it.

Not that I have been able to figure out the magic that gets you the ability to downvote, but I don't really feel the need.

[DeusExMachina]

There is a Karma threshold to be able to downvote or flag a comment/submission, so you simply don't see the option yet.

But indeed it sinks discussions, since the points are one the ways (not the only one) to sort comments.

[wtracy]

Apparently it has to do with how much karma you've accumulated. I magically got the ability to downvote some time last week, without any effort on my part.

[SomeCallMeTim]

You're just over 500 karma; I'm around 140 as I write this. So I guess I have a ways to go. :)

Not that I'm really worried about it one way or another, though.