Just like anything else they are subject to abuse. I take them sometimes when I absolutely must get to sleep and find I can't for one reason or another (too much light, noises or alertness). I get weird dreams every once and a while on them too. Almost lucid and sometimes too real. Great rested feeling when I wake up though.
It's not a one-size fits all drug where you'll get addicted or abuse them by merely using them. It's just like alcohol or any other drug. If you find yourself using them too often, stop. Try not to use them unless it's unavoidable or you have a sleep condition.
As much as I'd like to have crazy weird dreams and wake up like that all the time I'm not going to be dependent on it either.