As the financial incentives to participate increases, so will the amount of spam/bot posts. Even just bot zapping is a possibility that can warp behavior

Even if spam/bots can be kept in check, there's a big question as to whether post quality can be maintained when the site becomes more popular and mainstream.

Finally, there is the question of long run sustainability. At some point, will you need to cater to advertisers (and thus maximize throughput over quality) in order to keep the site running?