Since unrefereed papers do not `count' on an academic c.v. (and they should not), I must explain why I occasionally publish in unrefereed vehicles.
I have recently accepted the position of Editor-in-Chief of the ACM Sigsam Bulletin (Communications in Computer Algebra). Under my leadership, we have begun to publish formally reviewed articles. I have also chosen to publish several high-quality papers of my own in the Bulletin, as part of a general attempt to raise the tone. Of course there is no mechanism for reviewing the Editor-in-Chief's papers, so mine count as unrefereed.
This is a deliberate choice: I could submit my most recent three papers in the Bulletin to other refereed journals---I believe them to be of sufficient quality already, and my recent record of acceptances suggests that this belief is correct---but I choose instead to encourage increased readership of the Bulletin by publishing them only there. Such resubmission would not violate copyright: currently the Bulletin does not hold copyright of papers published there. I encourage you to read the Bulletin, to see if you agree with my choice.