From what I remember, that company in particular was bad news, but the premise of MLM is pretty sketchy. Often times, people who are involved in it have to end up stretching themselves financially in order to establish their businesses, and they are aggressive recruiters into their "uplines."
Here's a link to an article that's old (1996), but it takes a look at MLM from a critical POV. I used this in my research:
http://www.metroactive.com/papers/me...evel-9640.html