[jat850]

At the risk of further degenerating into meta discussion, I'll answer your question: Downvoting privileges are opened up at a certain karma threshold. The number has changed a number of times in the past and I believe it's currently at around a floor of 500-600 karma.

There are guidelines surrounding commenting/submissions here: http://ycombinator.com/newsguidelines.html

[Natsu]

Also, note that you cannot downvote anyone who replies to you.

[alanh]

Or posts older than a day or two, I believe.