Remi, the BIGGEST problem is with companies that clearly are benefiting from Open Source software but never giving back to the open source community. Be it contributions to the code or monetary donations, there is a severe lack thereof.

For example, companies that use open source software like LAMP severs (Linux, Apache, MySQL, PHP, Perl and Python) to run their corporate websites/intranet. These companies clearly benefit from open source development and should return the favor to the projects that they benefit from. Unfortunately this doesn't happen often enough. If it did, more open source projects would have the funding to pay some full time developers and progress more quickly. There are some exceptions though. One really good example is Google. Google is built on Open Source technology and does a great job of returning the favor back to the community through, both financial support and code contributions and even legal support. If more companies were like Google, the Open Source community would be ecstatic.

Another issue is the likelihood that some commercial software is illegally using code from open source projects. The proprietary barrier shields this from coming to light in most cases. These are the worst type of offenders. It's fine to use open source code in your projects, but you MUST abide by the license. Which in most cases, unless it's a BSD type license, you mush share your changes with the community.