Start contributing to GPLed open-source projects
Working on GPL'ed source code can be a major problem. It can cause taint to the closed source software especially if the projects are similar. Companies that work on both, like say Intel, normally firewall employees from open source and closed source projects for this reason.
C'est magnifique, mais ce n'est pas l'Informatique. -- Bosquet [on seeing the IBM 4341]