I'm one of the co-founders of BountySource and would be happy to answer any questions about our service. We're also on irc.freenode.net in #bountysource if you want to come chat!
I also don't know if all those 'joiners' icons add much, especially since many of them a blank github images. Social proof is great, but I would put something else in there instead. Something more action-causing.
Just a thought.