It is becoming very common for companies to ask developers for their Github page as part of the recruitment steps. Some companies will even review open source projects and look for active committers in order to find new people. Its very hard to judge developers from a CV, but the commits and engagement on a project demonstrates a developers skills and enthusiasm for their work.
Open source projects have long used online source code repositories to help share their work and attract other developers to their projects. If developers can get hold of the source code easily, then they are more likely to play with it and get involved.
With the advent of DVCS and the notion of pull requests, it has become really easy for developers outside of the project to get involved. The more pull requests you submit to a project, the more likely you will be invited onto the team and take on greater responsibility.
Help people find you by adding your github account to coderwall. Add yourself to companies and communities to help find opportunities to collaborate.