Currently the carreers.stackoverflow profiles only allow open-source projects to be mentioned in your "projects" section.
Problem I see
This does not represent a professional developer's portfolio. Most developers spend a major part of their time working on commercial projects. Running a popular website or having created (and selling) a useful product/service is - in my understanding - much more representive than a free-time open-source project. Also keep in mind that some of us have created software that is used by thousands or millions, but still not open-source.
Open this section for simple listing of websites, companies, products, etc. the user has created or was part in.