If they had fanfic back in the Dark Ages, I bet the most common question readers would ask is, "Can't you put a catapult in this story?" No, I'm sorry. That would violate canon.
Many people think that gen stories are dull. Dull? Is it "dull" when Jim gets bitten on the forehead by an ant, and at first it doesn't seem like anything, but then the bite gets worse and worse, so Blair takes him to a doctor, and the nurse tells them to wait, so they sit down and wait, and wait, and wait, and wait, and then finally Jim gets to see the doctor, and the doctor puts some salve on it? You call that dull?
When this woman I met at a slashcon asked whom I liked better, Vecchio or Kowalski, I said, "I like mayonnaise." She just stared at me, so I said it again, louder. Then she left. I guess she went to try and find some mayonnaise for me.
I still remember the first fanfic I ever read, where Schillinger killed Beecher and nailed his skull to an old board. Then he spun it round and round, like a wheel of fortune, and no matter where it stopped he kept yelling, "Tadpoles! Tadpoles is a winner!" I thought it was an incredibly shitty story. But then, I had some growing up to do.
And then there's the one that's only meaningful to Sentinel fans: I don't think I'm alone when I say I'd like to see more and more planets fall under the ruthless domination of Prospect-L. These days I just like to substitute "Merry Lynne" for Prospect-L.
Also, kassrachel has given a heads-up about a fantastic DVD sale at Amazon.com--$14.99 for the entire first season set, for several different shows.