Another take on this
I use Linux as a desktop OS and can't afford (or justify) paying for RHEL, however rather than use something like CentOS I prefer to use Fedora.
That way you're not only getting something for free but by getting involved in the Fedora community you're also giving something back by supporting the next generation of RHEL.
For mine the community effort that goes into CentOS just ends up providing a free version of something that already exists (ie. RHEL), but Fedora is what breaks new ground and I'd rather throw my support behind that community.