I'm sure I'm not breaking any new ground in saying this (so many pages in this thread!), but my biggest fan fic pet peeve is when someone thinks up a character and then writes a fic to glorify them. Essentially, the idea behind such a fic would be to show off how awesome the character is. This can be at the expense of story, it can be at the expense of believability (so far as believability in Star Wars can go), it can lead to character assassination for others (particularly canon characters, to show how super awesome the original character is), and so forth. To me, and to most writers I'd imagine, you shouldn't write anything unless you have something worth saying. Glory fics for your characters, where the only point is to illustrate your character's level of awesome, are not stories that generally have anything worth saying.