I've been reading and writing fanfictions since '08, and I find it's really quite enjoyable. Of course, my first ones were never that good, and in '09, I did stop writing entirely. But I got back into the swing of it in '10, and I haven't stopped.
I use fanfiction writing as an outlet when whatever piece of original fiction I'm working on doesn't go well, and I find it really helps. Because with fanfictions, you can take existing things and twist them to suit your desires. With original fiction, however, you need to make sure that whatever you're writing will be something a lot of people can enjoy.
I agree, most Drarry fanfics are terrible, but for every terrible one, there is an excellent one. And this applies to every fandom.
However, there are some fanfcitons that should have never seen the light of day. My Immortal, anyone?