I've never written fanfiction. It's only in the past year or so that I've read any.
Before I read any I assumed it was all poorly-written rubbish, but you know what they say when you assume things ... that you've supposed something to be true without any evidence (that's what they say, right?) Don't get me wrong, a lot of fanfiction is pretty awful; after all, liking a television show, film or book doesn't mean you'll be any good at writing about it.
So imagine my surprise when I discovered that there's a lot of fanfiction out there that's actually really great. That there are people who can take characters whom they didn't create and write interesting, clever and compelling stories about them. So far I've stuck with what I know and have only read 'Stargate' and 'Sanctuary' fanfictions, but I'd be open to suggestions if you've found (or even written) some gems.
Question: What are your thoughts, good, bad or ugly about fanfiction?
(N.B. Fanfiction.net is an excellent place to start if you're interested in reading fanfics. They have pretty much everything there.)