Most of the development jobs I have seen do not require a portfolio. They have a set of requirements and they verify that your resume meets those requirements. During the interview, they typically ask you questions to confirm that you are capable of doing the job.
It is possible that an employer will investigate you on the Web before hiring you. They will see your postings on Stack Overflow, LinkedIn, Facebook, blogs, etc.. If they go this route, they will probably judge you based on what they see.
In addition, it is also possible that someone will find you through your online contributions while searching for job candidates.
So in short, it is definitely not required (outside of design), it can certainly help you (if you do it well), and it can also hurt you.
EDIT: I would also suggest a STRONG mental portfolio so you can whip out diagrams and code snippets relating to your previous programming success stories. Nothing hurts worse than drawing blanks when asked to draw something on a project you haven't looked at in two years.