Right now it's a victim of DNS (Domain Name Service) spoofing. This means that a malicious party is trying to steal traffic from FFn by purchasing a very similar domain.
Correction:
The new "fake" site that people are seeing still belongs to FanFiction.net—they just misconfigured their servers and are not redirecting traffic from the bare fanfiction.net to the main site at www.fanfiction.net. There is likely no malicious agent. Didn't mean to scare anyone! Just wanted to let people know the site wasn't deleted!
So if you want to read fanfiction and not see leaves, you have have to type out "www.fanfiction.net".
Not to act all high and mighty but if someone kept trying to trick me into taking my meds by hiding it in a spoonful of peanut butter I wouldn't really for it more than like 3 or 4 times maximum