I really want to downvote on steemit. The game theory mechanisms on this site encourage a huge amount of low quality posting on the off chance that something gets an almost accidental or stray upvote or that some bot ring will come around and throw you some cash.
If you could downvote bad materials as well as upvote that might discourage users from constantly spamming the system. Either that or some sort of rate limit on the amount that you could contribute until you receive a certain amount of upwards posting. This type of scarcity mechanism would also encourage users to really focus on making high quality posts rather than just constant spam.
I'm also investigating other ways to game the steemit system to stay tuned for more details.
Note: After trying to post this I received a "You can only post once every 5 minutes error". Well done steemit! That's a good start.