For the most part I would say negative. Years ago, when Survivor started it was fun to watch the people try to survive, and see how they developed their camp etc. But then the genre took a turn to nasty offerings like Toddler and Tiaras, or the Kardashians. I think those kinds of shows are total crap. And I am like everyone else, if not careful I will get sucked into them.
All of the reality shows now seem to thrive on backbiting and conflict. It gets tiring. I can't see that as having a good effect on society.