The sad truth is that a lot of the projects offering bounty campaigns are doing so because their project sucks. Yes there are some decent ones and most of them are ran by good managers such as Amazix or g0blin.
However, many projects will never go anywhere and they want you to work to promote them and pay in their own token because it costs them nothing.
Quality is better than quantity, one or two good projects are better than many bad ones and you need to do your research exactly the same as if you were investing your own money.