Yes had heard of @steem-bounty and participated at thedarkhorse #payitforward initiative. Steem bounty is useful when you need engagement, especially when there is a topic to be discussed, or questions that need answers.
There are many steemians who go around hunting for steem bountied posts to leave comments. That is good for the system and community. However, not all posts are suitable to use steem bounty. Too much of them will attract more spammers and abusers.