What you guys think about debt Settlement/Negotiation Programs?

I have like 40K credit card bills and want an easy and quick way out of them. I also need to keep my credit in a good shape so i am looking for a program to work with to help me to get red of debts. I interviewed a few debt settlement companies ( http://www.cydebt.com/home/homepage.shtm) and they told me that they can reduce my debts to 15K and wouldn't mark my credit. So what is the disadvantage of these companies and why everybody thinks that they're rip off. I also can't understand one part... what's will my creditors do if i don't make any payment?