I don't punish for bad grades that result from difficulty in a subject, but I do punish for laziness/poor work habits.
Not turning in assignments, waiting until the night before a project is due and then telling a parent you need posterboard or some other type of help, not studying for tests when they give you a full week's notice, slopping together a paper last minute (turning in what amounts to a rough draft): all are punishable offenses in our house.
It's not about the grade, it's about their work ethic.
Punishments might include a required "study time" each day or much closer parent supervision of homework completion. Normally, we do not check their school day timers or look over their homework. But, we will if they are getting sloppy. And, if we felt electronics were the cause of the distraction, they would have to earn that priveledge day to day by following through on their homework. We do not typically control how much time they spend on the computer/tv/game systems.
I don't feel our punishments are anything dramatic, just what we consider logical consequences for demonstrating poor time management and sloppy work.
If they want to be in charge of their schedule (study time vs. play time), then they need to "be in charge." Otherwise, we will step in and take charge.