The problem with bountysource is that the bounties are quite low for the amount of work involved. Working a week consulting on the customization of open source software for a business will usually net far more than the largest bounty on there. (And those large bounties are significant, highly-specialized tasks.)

I think the bounty model could work well, but on all the projects I've seen it implemented on, it acted more like a tip mechanism for the core team than a way to attract professional freelancers to contribute, because of the low value of the bounties.