I would never steal a whole story from someone, but maybe funny quotes or something, I would 'borrow'. (Mainly, from HP books, even some fanfiction if it is someone I know who wouldn't care)
Anyway back to the topic, I do it so I can practice really. I roleplay a lot, and somehow fanfiction shows that, so I post it to see how it is.
My Current Addiction: Berries and Cream Dr. Pepper, and the Gossip Girl series.