Yeah, I was looking after my cousins for a while (long story) a 17 year old girl, 14year old girl and a 6 year old boy. Everything was going okay, but my usual positive reinforcement wasn't really working with the 14 year old. She refused to help around the house, spent every spare minute she had on her PC in her bedroom, she wouldn't feed or walk the 9month old pup, that she asked for and a bunch of other crap that I really don't want to get into.
Anyway.. After playing nice for a solid 3 weeks, I sat her down and informed her that unless she started doing her homework, looking after her dog, doing her chores, etc etc, then she would start losing privileges. She didn't believe me. So I went into her room one day with my handy screw driver and removed the plugs from the computer, her tv, and I even took the battery out of her blackberry. She learned her lesson.
Eventually she did get it all back, but only after she stopped being such a lazy git.