Wow this is a good topic. I think that if either party gets re-married the income should not count. I really feel that if one party is living with their parents then the income of the parents should not count.
Now all of this talk about not having to pay at all! If you don't want to pay then don't play. The child's well being is as much the man's responsibility as the woman's. Yes, I am a man. If your ex leaves your sorry butt and she keeps your children and then betters herself by going back to school, or starts her own business, or even wins the freaking lottery and becomes a millionaire, you should still have to pay whatever the court ordered because it is your responsibility. Even if you can't keep a job making more than seven bucks an hour shoveling horse crap at the track.
All of these worthless Dad's out there that complain about it try to remember what the money is going for. Kids need shelter, food, education, clothes. Remember the money needed for birthday parties, Christmas, vacation, sleep overs, sports, clubs. Maybe you could not keep a job for these things when you where married either and that is why you are divorced now. Well just because she found a man that is descent or found a way to do it herself does not mean you should get the free ride.