I did used to publish fanfic online, though not in quite some time now. I haven't written any since I was a freshman in college. I would not, however, use it to expand my bibliography, as you say. It was wonderful writing practice and great fun at the time, but I've kinda closed the book on all my fan-fic writing. No one wants to read a 15-year-old's fangirly Beatles fanfic, and I'm not planning on taking it up again any time soon.