Fanfiction.net annoyingly bans, among other things: stories in script-form, stories in second-person (or "you-fics"), fics involving real people, and anything they deem "interactive", up to and including responding to readers' questions. As a member of the PPC once declared of scriptform: "If it was good enough for Shakespeare, it's good enough for fanfiction."
It also doesn't support many punctuation marks, such as *, <, >, , , and /, despite several of these being vital to certain fandoms, for example as the <> "thought-speech" speech marks in the Animorphs fandom. It also removes any links or email addresses in stories.
The site furthers its bad reputation by randomly banning a lot of really good stories for absolutely no reason. Its reporting system also doesn't seem to be regulated, as it can and has happened that one person has reported another's story because of a grudge rather than the story having anything wrong with it, resulting in the story's unfair deletion.
Fanfiction.net is popularly known as "the Pit of Voles", or just the Pit. Have you ever heard the saying that a thousand monkeys working at a thousand typewriters would eventually produce the works of Shakespeare? Well, if that's true, then common wisdom is that whatever's writing the stories on ff.net can't be monkeys.
"No! But it's at a really good bit!"
Considerably less impressive now due to restrictive rules placed on the types of entries allowed in recent years.
Motto: "Unleash your imagination and free your soul." No longer applicable.
Guy 2: Dude, it got deleted.
Guy 1: You serious? Ok, what about this awesome one?
Guy 2: Nope, sorry.
Guy 1: Well... what about that Super Dragon Ball Z With LOTR story?
Guy 2: Uh, yeh...
* FanFiction.net caused a controversy a while back after banning all fanfic rated above R (NC-17). A number of fans boycotted the site after losing their fiction, and several others simply began assigning an R rating to graphic fic.
Decisions such as reinventing the search system when it was already good. Now you'll be lucky if any search you make with more than one word come up with accurate results. Other decisions include taking away NC-17 rating, banning stories about real life people, and banning stories that doesn't fit a certain format. What's the point of "unleashing your imagination" if your imagination is restricted?
Also, there are a number of website problems there. The usual and least believable explanation is something along the lines of "server upgrade".
Despite this, people don't have much choice because FF.Net still has the most stories and the best interface.
Don't me wrong, I read/write for Fanfiction.net quite often, and if you're patient, you WILL find something good and worth reading. You'll just have to dig through a lot of garbage first.
Fanfiction.net also has a sibling website, Fiction Press, which is for original content.
Often abbreviated as 'Fanfiction' or 'Fanfic'
"Check this out! After an hour of browsing on Fanfic, I found a story that's actually really good!"