Reporting what feel like two bugs in pybombs that only arise in CentOS. You won't encounter these in Ubuntu.
1) Minor feature/bug: The config.defaults file does not contain rpm in the satisfy order list. It needs to be added manually.
Major bug: I'm calling this major because it prevents installation on CentOS and is very difficult to work through for newbies. When installing from source is the primary install option, the recipe files for pygobject and pygtk point to incorrect file locations. The rpms for CentOS 6.6 don't contain these packages so install from source is the only option.