Are the thresholds for things public? I was expecting (based off what, I can't remember) to be able to downvote at 100, but I'm now on 2xx and I still can't.
The thresholds are non-public, and adjusted from time to time based on pg's perception of the growth of the site. My impression is that comment downvotes seem to occur about 500 karma these days. There's no post downvote that I know of.