Plot contrivance: All the city, including the cops and criminals, are looking for Kick-Ass. They can't seem to find him even though he has a Myspace profile updated from home. Big-Daddy actually finds him by using his IP address. Why can't the cops and criminals find him too ? Did they all fail to hire a single computer engineer ?
Unaddressed Issue: When Hit-Girl saves Kick-Ass, she had to leave her hideout and find the factory relatively quickly - even though nothing in the film hinted of a way for her to know where to go.