As recently (re-)suggested by Kaj Sotala, posts now have much larger effects on karma than comments: Each up or down vote on a post is worth 10 karma.
Negative votes on posts have had karma effects all along, but for some reason Reddit's code imposed a display cap (not an actual cap) of 0. This violates a basic user interface principle: things with important effects should have visible effects. Since this just got 10x more important, we now show negative post totals rather than "0". This also provides some feedback to posters that was previously missing. Note that downvoting a post costs 10 karma from your downvote cap of 4x current karma.
The minimum karma to start posting has been raised to 50.
Thanks to our friends at Tricycle for implementing this request!