I've enjoyed some fanfiction, but on the whole they usually can't keep my interest. The only time I think fanfiction is really helping an aspiring author is when they base the story on entirely new and different characters within that same world, learning to flesh out someone of their own design.  Sadly, most of the fanfiction I've come across is mostly 'plot for the sake of pairings', or simply rehashing certain moments in the book/show/etc to change a relationship.

I like a wee bit of romance but I prefer not to read fanfiction that's only driven by a romantic pairing, where if you took one of them out of the story the entire plot would fall apart. Unless I'm curled up in a blanket intending to read a romance novel, I'm just not interested in that.