Pat David is a member of the GIMP team who has written extensively about using GIMP for photo processing (along with other software and techniques).
A few years ago he found the community and resources lacking for doing photography with Free Software. What was available was low-effort and low-quality mostly. In an attempt to address this, he created PIXLS.US. It's a community focused on photography using Free Software tools, that hopes to remove barriers to collaboration between projects, users, developers, and hackers.