I wrote two related articles:

1. The steemit curation nightmare: plagarism, spam bots, ghost profiles and cross-posting
2. Curation rewards are still broken

The new curation system penalises those you upvote quickly. In the first thirty minutes, the curation award is shared with the article author. The quicker the upvote, the more goes to the author, starting at 99%.

The problem I pointed out is that bots could collude. Likewise, others have pointed out that it's not that hard to get the bots to more time. Of course, if others vote in the meantime, the bots will be awarded less of the curation reward. Perhaps bot authors are just voting quickly and hoping to win by covering as many posts as possible.