This is an interesting approach but not all talented developers partake in open source projects.
Facebook has a nice social graph but no angle on programmer socialization. Github's API can let you infer which open source languages I dabble in, but not at all what I do at my day job. Good luck to you though, I'd love to see the product.
The market is hot right now and it would be pretty nice to be able to show some of the programs that has been written.
Why would I release my software on github for free, when I can release it on Google market for money?