According to my-brother-the-lawyer there is always some danger in fanfic. There is more danger in fanfic that is actually tangible and being passed hand to hand. There is most danger in fanfic that is being charged for. There is a reason I don't archive anywhere except my own journal since I also have the desire to publish orignal fic some day (when I finish the bloody novel, anyway).
That being said, you have to make your own risk assessment, which ultimately depends on how paranoid YOU are. :P