For practical purposes, I think you'd be surprised. I've downloaded a few things in my time, and no one's ever come knocking on my door. The feds really, truly, don't care that much unless you're running a massive operation.
...Don't tell anybody...but...
I'm filling up my third 1TB hard-drive with pirated goods.
I also still can't find my old 250 and 500gb hard-drives, chock full of materials...I'm also constantly burning movies, and giving them to my friends.
I'm a bad person...