We use promoted listings and are quite happy with it. Initially, we went with $2/day, but in the past month we have upped it to $4/day and have also seen a corresponding increase in traffic. Generally it seems that for every $1 we spend on promoted listings we will earn $4 in increased revenue. This means that our profit is significantly lower for those items; however, it may drive more sales over time (people favoriting now to return later, Holiday season etc.).