Anyone have any horror stories from using a debt consolidation company?

I am single guy, with a house, looking to lighten the load on my wallet. I was hoping to combine a small loan, an old credit card bill and my mortgage into ';one lower monthly payment'; like all the ads claim, but I want to know if there is a down side. Also, I am about as financially challenged as they come so keep any responses in easy-to-understand terms. Thanks!